Archive Your iOS Device Backups With iTunes
Always back up your data and files to iTunes before you install a prerelease version of iOS. Then archive the backup. If you back up to iCloud or if you don’t archive your backup, you won’t be able to restore from it if you go back to current version of iOS.
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4. When the backup is complete, go to iTunes > Preferences > Devices.
5. Find your device’s backup and Option-click the backup. Choose Archive.
This should read “Control-click the backup.”
