There are two ways to restore your iPhone from backup. One way is through iTunes and to backup this way, connect your phone to your computer that has your iTunes information. When your iPhone is connected and the iPhone management screen is available, choose Restore. Walk through the prompts to quickly restore everything that was backed up to iTunes.

The second way to restore your iPhone from Backup is from iClouds backup if you have set up an iCloud account. To do this, go to Settings > iCloud > Storage & Backup and choose, Backup Now. If you have any issues, make sure your iPhone is fully charged and restart it before you attempt to back it up.

Resource: About Apple