How can I get Apple's new iOS 9 operating system software on my iPhone? And is my iPhone fast enough to run iOS 9 without slowing down? Should I update to iOS 9.1?

iOS 9 has just arrived, followed by several updates including iOS 9.1. If you go to Settings > General > Software Update you should see the download. But be cautious! Make sure you have a backup and expect the download to take quite a while. Read on to find out more.

How to update to iOS 9: The complete guide

iOS 9, the new operating system software for iPad, iPhone and iPod touch, was unveiled during WWDC 2015 in June and finally became available to all on 16 September. You've probably got three questions: can I update my iPhone or iPad to iOS 9, should I update my iPhone or iPad to iOS 9 and (if the answer to the first two is yes) how can I make the upgrade.

We'll address these questions in that order in our complete guide to iOS upgrades. We've also got details on how to install iOS 9's subsequent updates including iOS 9.1, and whether you should let Apple update your iPhone for you overnight.

Sections in this article:

NEW: Watch out for the overnight iOS update bug that has been turning off alarms around the world

With iOS 9, Apple is trying to encourage more users to install the incremental updates that provide fixes and small improvements by offering the chance to install them for you overnight when you are sleeping. If you're prompted to update your iPhone while you're using it, Apple now lets you choose 'Later,' which will then specify a time period during which it will update automatically for you if you've got your iPhone plugged in to a power source, which most people do overnight anyway.

When Apple prompted Macworld's own Ashleigh Allsopp to update to iOS 9.1 and offered me that 'Later' option, she decided to make the most of the convenient new feature. She expected to wake up in the morning as usual to an updated iPhone. And indeed she did, but she woke up more than an hour after her alarm was scheduled to go off. The update had worked brilliantly, but her alarm had been deactivated, causing her to be very late for work.

She's not the only one. Users have taken to social media and forums to express their annoyance with the issue, which we consider to be a bug, and many have been late for important meetings and school.

Therefore, we'd only recommend choosing the later option if you don't have to wake up at a particular time in the morning, or if you can set another alarm on a different device!

Read: Advanced iOS 9 tips

How to update to iOS 9: The basics

iOS is the operating system software that runs on iPad, iPhone and iPod touch devices. It's the underlying framework that organises, launches and runs other apps, and can perform a number of features of its own. iOS 9 is the newest update to iOS, and launched officially to the public on 16 September 2015.

If you've got an iPhone 4s (or later), an iPad 2 (or later), either of the iPad mini models, or a fifth-gen iPod touch, your device is officially rated as iOS 9-compatible, and you can update to iOS 9 for free. (We discuss the list of compatible devices in a little more detail in the next section.) You can also access the iOS 9 beta.

We discuss iOS 9 as a single entity for most of this article, but we should quickly acknowledge that a number of smaller point upgrades will be released throughout its year-long lifetime, and some of those have already arrived. Don't expect any big differences between these - mostly these will incorporate security updates, fixes and minor tweaks. When you update your device to iOS 9 you will automatically get the most recent version that is available.

How to update to iOS 9 on iPhone or iPad

How to update to iOS 9: Which iPhones & iPads can get iOS 9?

We've discussed this question in considerably more detail in a separate article: Can my iPhone or iPad run iOS 9? But we can summarise things here.

Essentially, if your iPhone is an iPhone 4S or later, if your iPad is an iPad 2 or later (or an iPad mini or later) and your iPod touch is fifth-gen, you're safe - Apple has confirmed that all of those devices support iOS 9. Needless to say, the new iPhones - the iPhone 6s and iPhone 6s Plus - and the new iPad Pro will all come with iOS 9 pre-installed, so you won't need to worry about updating those devices to iOS 9.

Which iPhones & iPads can get iOS 9?

We feel compelled to point out that devices on the borderline - the somewhat older iPhones and iPads that only just make it on the list - have in the past often struggled to run new software effectively. The iPhone 4s was the oldest iPhone that was allowed to run iOS 8, but lots of users found that it slowed down as soon as the installed the new software. iPhone 4 owners had a similarly negative experience when they upgraded to iOS 7.

These devices were powerful enough to run the new version of iOS - but only just. And you don't want to be in that position. We therefore used to advise people not to update their iPhones and iPads if they were at the older end of the list of compatible devices. It's generally very hard to downgrade from one version of iOS back to the previous one.

That said, normally iOS gets more and more demanding to run each year; but Apple claims iOS 9 isn't just level with iOS 8, it's actually less demanding. In other words, devices that were starting to run a little slowly with iOS 8 may even speed up when upgraded to iOS 9.

Read next: iOS 9 vs iOS 8 comparison review

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How to update to iOS 9: Should I upgrade to iOS 9? What are the benefits, and will iOS 9 slow down my Apple device?

This leads us to a harder question: even if you're allowed to upgrade, is it a good idea to install iOS 9? Are there any reasons why you wouldn't upgrade to iOS 9?

Should you update to iOS 9? The cons

First of all, bear in mind that upgrading iOS tends to be essentially a one-way journey. It's always extremely hard (if not impossible) to go back to the previous version afterwards, so be sure you want to do this before starting the upgrade process.

So you'll probably be stuck with the new OS if you update. But are there any actual down sides in the way iOS 9 will work?

The first is speed. While Apple always works on streamlining iOS and making sure it runs smoothly, it has to be said that the past couple of updates have both slowed down older iPhones and iPads. As we said, iPhone 4s owners were not impressed when iOS 8 noticeably slowed down a lot of their devices, so the same could be true for iOS 9. Apple says this year will be different, but we'd still advise caution until you've heard from people on the same hardware as you that iOS 9 runs okay.

There are no major changes in the visual design department, so you're unlikely to be upset by changes to the way iOS 9 looks compared with iOS 8. When iOS 7 launched two years ago, many users were horrified by the radical graphical redesign, which took a while to get used to and still annoys a minority of iPhone and iPad owners. That year we advised people to spend time with borrowed iOS 7 devices if they could, and see if they got used to the look of the OS after a week or two - generally interface changes feel earth-shattering at the time, then before you know it you can’t remember how it used to look.

But in this case, as we say, there's no significant visual rethink. iOS 9 looks very much like iOS 8, which in turn looked very much like iOS 7.

Other than that, we don't expect there to be any major worries for those expecting an update.

Should you update to iOS 9? The pros

Of course, the pros are that you're getting a new operating system that comes with loads of new features. You can find out about the new features in iOS 9 in more detail in our iOS 9 preview, but below is an outline of what you'll be getting.

New features: An exciting new 'Proactive' Siri-activated personal assistant, rather like Google Now; pubic-transport directions (and other new features) in an improved Maps app; new and improved Multitasking (which is split screen on iPad Air 2), a new News app, an overhauled Notes app.

Design tweaks: As we said, the design changes aren't earth-shattering, but the designers have smoothed a few things over. They keyboard has been slightly redesigned and improved, for example, and some of the visuals are very slighty different to make them easier on the eye.

Fixes, tweaks and stability stuff: Boring but useful, particularly the battery life enhancements that should mean an hour extra power and a new low power mode to extend battery even further.

Future-proofing your device: This will become important in the future. Generally app developers try to make their stuff work with a wide variety of devices, but there will always be a limit. Check your favourite app on the App Store, and under Information you’ll see something like 'Requires iOS 6.0 or later'. In a few years apps will start to say things like 'Requires iOS 9.0 or later'.

Read next: 31 brilliant iOS 9 tips

Should you update to iOS 9? Conclusion

If your iPad or iPhone is up to it (and really up to it - not just officially rated as iOS 9-compatible), you should probably update. Even if you don't care about the new features, the boring stuff - such as bug fixes and compatibility with new apps - is important.

But take the decision carefully, because you probably won't be able to go back

See where your iPhone or iPad sits on the chart of compatible devices above. If it's only just new/powerful enough to run the new OS, you need to find out if there will be any speed problems. See how people with the same model as you get on.

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How to update to iOS 9: Important steps to prepare your iPhone or iPad for the upgrade

We're about to walk you through the update process. But before we get to that, here are the steps you should take before you click yes on that update alert. (My colleagues look at a couple of aspects of this in a little more depth in a separate article: How to prepare your devices for iOS 9.)

1) Back up your data

Use iCloud or iTunes to back up your iPhone, iPad or iPod touch. If you don't do this, and you find that messages or photos disappear from your iPhone after the update, then that's your look-out.

Beware: the backup will include purchased music, TV shows, apps, and books; photos and video in the Camera Roll; and device settings, but it won't include anything you synced from your computer. To re-sync that stuff you'll need to sync with iTunes. For that reason we recommend backing up to your computer as well as iCloud.

2) Save a compatible copy of iOS 8 in case you change your mind

You may change your mind and decide you want to downgrade from iOS 9 to iOS 8, and this will be easier if you make sure you've got a copy of the latest version of iOS 8 compatible with your device.

You see, Apple 'signs' versions of iOS, which in effect tells your iPhone or iPad that the version you want to use is okay for that device. As long as that version is signed, you can install it on your iOS device, even if it's earlier than the one on there at the moment. (Traditionally, Apple stops signing old versions of iOS only a day or two after releasing major updates, so you'll need to act quickly if you want to go back.)

If you have a copy on your hard drive you will find it, by default, by following this path: youruserfolder/Library/iTunes and then select the Software Updates folder for your device. (Access the Library folder in your user folder by holding down the Option key in Finder and selecting Go > Library.)

Your Mac may have deleted this file, however. If so, launch your web browser and search for download ipsw. You'll find a number of sites offering links to the file you need. Make sure you get the right one for the device you use.

3) Make room on your device

If you have limited space on your phone you may not be able to perform the update - it's a fairly hefty download. To get ready, you can remove content you no longer need, which is a good idea in any case. See our guide to making room on your iPhone or iPad

Our iPhone required 5.8GB of space to be available in order to perform the iOS 8 update - since our iPhone is only 16GB this wasn't really an option so we opted instead to update via iTunes on our Mac. More on that process below.

For iOS 9 we're hopeful that the install file will be a bit smaller. That's what Apple says, anyway.

4) Update iTunes on your Mac or PC

A couple of years ago people updated iPhones to iOS 6, only to discover that their iPhone or iPad could no longer talk to their Macs because they were running an old version of iTunes. This was made worse if they couldn't actually update to a version of iTunes that was compatible because they were running Mac OS X Leopard on their Macs.

It was a big enough issue for Apple to actually start selling Snow Leopard again because it was the only way to get the Mac App Store - which is the only way to update to later versions of the Mac OS.

Read next: How to get Snow Leopard.

5) Plug in your iPhone or iPad

Make sure you plug in your device to a power source. If you run out of battery mid-download you may corrupt the iPad or iPhone.

6) Make sure you're connected to Wi-Fi

Be sure that you are downloading over Wi-Fi and not via 3G or 4G, or you may end up using up all your data for the month. Read our guide: how to stop running out of cellular data.

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How to update to iOS 9: How to upgrade to the official version of iOS 9

The final official version of iOS 9.0 will became available on 16 September, and is available to owners of all compatible iPhone and iPad models from then on.

If you decide that upgrading is right for you then how do you upgrade to iOS 9?

It's actually very easy. You should get a notification informing you that a new version of iOS is available for you to download; all you need to do is confirm that you're happy to do this. Download the iOS 9 install file, and then install it; the process should take a few hours - don't worry, this is normal - but the length of time depends on the server traffic and how well Apple is coping with it. It's got much better since the huge delays people faced when updating to iOS 6 on launch day.

Haven't got a notification that iOS 9 is ready? Take a look in the Settings app and scroll down to General. Tap Software Update (the second option down), which will have a little '1' if there's an update for you.

iOS will think for a moment and then present you with the update, including the amount of storage space required (you may need to clear some space before downloading) and a link to a 'Learn more' article that tells you about the changes. Simply confirm you wish to upgrade and follow the steps.

If everything is working as it should, updating to iOS 9 should be extremely simple and user-friendly. It's also free.

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How to download and install iOS 9 on your iPhone or iPad: Step by step

The update is pushed out to your iPhone or iPad automatically. You just need to go into the software update section of Settings and accept the update. Hopefully you will be lucky and it will work first time.

1) Go to Settings > General > Software Update

This will force your iPhone or iPad to check for the latest updates. (You may get an alert telling your that iOS 9 is ready, in which case you'll just need to tap download.)

2) Tap Download

Your iPhone or iPad will start to download the update.

3) Leave the update to download in the background

Once the download has finished you will receive a notification saying an update is available for your device.

4) Tap Details

This will take you to Settings > General > Software Update.

5) Tap Install Now

The iPhone or iPad will now start to install the iOS update. 

You can choose to leave the installation for later. Settings will display a notification badge until you have installed the update.

How to update to iOS 9 if you haven't got room on your iPhone/iPad

A common problem when updating your version of iOS is to find that there isn't room on your device for the install file. One solution is to delete lots of files from your iPhone and make room, then put them back afterwards. (Apple says it will offer an automated tool to do this for you when iOS 9 launches.) But another solution is to update iOS via iTunes on your Mac.

We explain this relatively painless process in a separate article: How to update iOS on your Mac

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How to update to iOS 9: Common problems when updating iOS, and how to avoid/fix them

Updating to iOS 6, iOS 7 and iOS 8 in the past has been difficult in all sorts of different ways. In this section we'll try to offer tips on avoiding or fixing these problems if you encounter them.

We had a complete nightmare installing iOS 7 in 2013 - it took us all night. We had hoped things might go a bit smoother in 2014 with the launch of iOS 8. But unfortunately not. Again, many faced installation dramas because Apple's servers seemed unable to cope with the sheer number of people trying to access them to get the download. So if this was your experience with iOS 8 it's not a huge surprise, and you shouldn't feel like you're alone.

One thing is for sure: if you chose to update as soon as iOS 8 launched you were probably in for a long wait because the first few hours of an update are always the busiest time on Apple's servers. If you're like us you tried to update to iOS 8 pretty much as soon as it was launched, and probably found that it was going to take hours (ours said 14 hours). Perhaps you even saw error messages and warnings that the update had failed.

If you want to avoid having a long wait for the download, we recommend you wait for a day or two, both because the rush will have died down and because some initial bugs and problems that weren't noticed in the beta testing phase will have been patched.

All that presumes you had enough space on your iPhone to start with. The main issue encountered by those trying to update was the fact that the iOS 8 update requires a lot of space to be available on your iPad or iPhone. When we tried to update it said we needed 5.8GB of storage available, even though it claimed that the iOS 8 update itself is just 1.1GB. Why does it need so much space? This is because it downloads a compressed file, unpackages it and then installs it. You need the space for the unpacking and the update. It also needs enough space for iOS 8 itself.

If you don't need to free up a lot of space you may be happy to delete a few images from your Camera Roll or some of your music. You might find it useful to read our guide to saving space on your iPhone here.

Luckily you don't really need all that space to be available - you can download the update via your Mac or PC. We show you how to do that here. Also read: How to improve iPhone battery life.

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