You can update iPhone software in Settings, or by using iTunes. You can also erase or restore iPhone, and then use iCloud or iTunes to restore from a backup.
You can update software in iPhone Settings or by using iTunes.
Update wirelessly on iPhone. Go to Settings > General > Software Update. iPhone checks for available software updates.
Update software in iTunes. iTunes checks for available software updates each time you sync iPhone using iTunes.
For more information about updating iPhone software, see support.apple.com/kb/HT4623.
You can use iCloud or iTunes to restore iPhone from a backup.
Restore from an iCloud backup. Reset iPhone to erase all settings and information, then sign in to iCloud and choose "Restore from a Backup" in the Setup Assistant.
Restore from an iTunes backup. Connect iPhone to the computer you normally sync with, select iPhone in the iTunes window, then click Restore in the Summary pane.
When the iPhone software is restored, you can either set it up as a new iPhone, or restore your music, videos, app data, and other content from a backup.
For more information about restoring iPhone software, see support.apple.com/kb/HT1414.