iOS 9 is almost here, and we're getting ready for the launch. We've been enjoying the iOS 9 beta for a while now, and needless to say, we'll be downloading the official public version of iOS 9 as soon as it appears. If you feel the same way you've come to the right place.

For most queries related to the iOS 9 update process, your first port of call should be our iOS update guide. This has all the advice you could possibly want, from preparing for the update, to the pros and cons of each version of iOS, to the possible problems you're likely to encounter and how to fix them.

This article is a bit more specialised. We'll be addressing one particular issue that lots of people have faced when updating to a new version of iOS: not having enough room on their iPhone or iPad to squeeze in the install file. (Apple says this will be less of an issue with iOS 9, both because its install file will be smaller and because there will be an automated tool to delete non-vital files and then reinstall them afterwards, but we can't imagine the problem will disappear entirely.)

To get round the problem of an over-full iDevice that can't fit in the latest iOS update file, we offer a simple and effective solution: update iOS on your Mac instead.

(For a more old-fashioned approach to this problem, see How to make space on an iPhone when you need it.)

Read next: 31 brilliant iOS 9 tips

How to update iOS via your Mac

This is what we had to do when it turned out iOS 8 required more space than we had available. You can view a video tutorial for these steps at the top of this article.

You need a lot of space to install iOS 8. When we checked General > Software Update we found that iOS 8 was 1.1GB in size but it required 5.8GB storage to be available to install.

Apple helpfully suggests that you can make more storage available by deleting items in Usage Settings, but that’s easier said than done, especially when you have a 16GB iPhone. We had just 1.4GB available on a iPhone 5s. Sure, we could have delete Music (3.6GB) and Photos & Camera (2GB) but that still wouldn’t be enough. And to be honest, we weren't keen to delete anything because we'd already slimmed down the iPhone considerably (having previously had a 64GB iPhone 5). Luckily there is another way.

Turning on the Mac and starting up iTunes gave us the message that "A new iPhone software version (8.0) is available for the iPhone "Karen's iPhone". Would you like to download it and update your iPhone now?"

Before clicking Yes, we quickly checked that the iCloud Back up was up to date. Last backed up on 14 September 2014 at 20.45 seemed a bit out of date, so we did a backup as that’s always a wise thing to do before updating. That took a few minutes.

Once backed up we clicked on Transfer and Update and the Mac began connecting to the iOS update server.

Then we clicked Agree to the software licence agreement. And when it asked for the passcode on the phone Touch ID was sufficient.

Here's where we wish it was quicker, when we tried this on the night iOS 8 launched, iTunes told us that there was 11, then 12, then 13 hours remaining. We're pretty sure that is longer than last year? We left it downloading overnight. Unfortunately by the morning the download had failed. Probably because the servers were overloaded.

This morning we started the download again. Things moved a lot quicker this time. Once the iOS 8 update had finshed downloading to our Mac, it then switched to updating the iPhone firmware, eventually restarting the iPhone at which point we had various set up options to run through before iOS 8 was ready to go.

You can follow the whole process in the video at the top of this article. It did take a while, but probably only about 40 minutes from beginning to end.

How much space does iOS 8 take after installation?

At the beginning of the installation we had 1.4GB of space available on our iPhone (although iTunes on our Mac suggested that there was 2.7GB available). By the time the installation had finished we had 839MB of space left according to our iPhone (and 844.9MB according to our Mac).

That suggests that the installation has taken up 561MB of space on our iPhone (or if you go with what the Mac said, 1.8GB. It seems a strange discrepancy and we will try and get to the bottom of why the iPhone thinks there is less space than the Mac.

We have run an app that we use to clear junk files (CM Security), that cleared 362MB of junk files, so now we have 1.1GB space left. So 300MB is all we've lost - presumably that’s how much bigger iOS 8 is than iOS 7.

We look at whether you should update to iOS 8 here, and ways to downgrade from iOS 8 here.

Find out what to expect from iOS 8 – read our iOS 8 review here.