You can restore the settings, application data, and other information from a backup, or use this feature to transfer these items to another iPhone.
Connect iPhone to the computer you normally sync with.
In iTunes, Control-click iPhone in the sidebar and choose “Restore from Backup” from the menu that appears.
Choose the backup that you want to restore from the pop-up menu, then click Restore.
If your backup is encrypted, you’ll need to enter your password.
After restoring from a backup, previous data is no longer accessible via the iPhone user interface, but it isn’t erased from your iPhone. For information about erasing all content and settings, see Resetting iPhone.
IMPORTANT: Restoring iPhone from a backup restores all data in the backup, including data for other applications. If you choose an old backup, restoring from it could replace the data for applications with data that is not current.