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.
Do also bear in mind that each incremental update to iOS 9 will take small amounts of space from your device. Such as how iOS 9.2.1 is a 100-300mb update depending on the device it's installed on.
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.
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.
How to update to iOS 9: How to upgrade to the official version of iOS 9
The final official version of iOS 9.0 was made 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.
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