Restoring a backup using iTunes may be done at any time. Before proceeding, make sure the latest version of iTunes is installed on the computer (http://www.apple.com/itunes).
Connect the iPhone to a computer using the supplied USB cable.
Note: If the sidebar is displayed, click the iPhone name under DEVICES.
Click Restore Backup.
Click the iPhone Name drop down list and select the desired backup.
iTunes will download any necessary files and restore the iPhone.
Once finished, click OK.
The iPhone is now restored.