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.
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.
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.
Sign up for CIO Asia eNewsletters.