Worth confessing the one drawback of iOS updates policy; Once you have updated there is no going back, they won’t allow you to revert to an older version.
If it helps, that's not quite true. It's just a bit more involved.
Firstly, you need to have a backup of your phone from before the update is applied. Assuming you have iCloud Backups enabled, you'll have one less than 24 hours old already.
After the update, should you wish to downgrade, all you need is a copy of the earlier version's OS image - the .ipsw file. These can be downloaded directly from Apple's update servers -- check out
https://ipsw.meThen, connect your phone to your PC or Mac and start iTunes (downgrades cannot be done over-the-air). Go to the phone summary page and look for the
Check for Update button.
Now, hold
Option (or
Alt on Windows) whilst clicking that button. You'll be shown a file selector. Choose the .ipsw you downloaded and your phone will downgrade.
You can then follow the initial setup process and choose the iCloud backup to restore from at the appropriate point. The UI clearly indicates which backups were made with each iOS version, and it won't allow you to restore a backup from an iOS version other than the one you've restored to.
A couple of notes:
- This will factory-restore your phone, hence the need to have a backup available to restore from.
- As noted, you *absolutely* need a backup available that was taken by the iOS version you want to downgrade to. iCloud backups might not cover all data, depending on how installed applications treat their data (apps can exclude their own data from iCloud backups). To ensure you have a *complete* backup, take one via iTunes, ensuring you enable backup encryption -- iTunes won't backup sensitive info to an unencrypted backup
- You cannot revert to any random iOS version. The .ipsw signatures are verified with Apple before installation, and they withdraw signing for old versions of iOS (more than ~1 year old, if I remember correctly). This isn't a problem in practice, since you'll be unlikely to decide to revert after several months of using the updated version.
Cheers,
Chris