It happens. You may lose your old phone, accidentally wipe your new one or may just get a new device to replace what you already have. In any case, you’ll want to restore your iPhone from a backup.
There’s an easy way to do this. Just plug the phone into iTunes, then right-click on the iPhone in the left-hand bar of the screen, then select “restore from backup”.
You’ll be given the option to choose which backup you want. Then, just follow the prompts, and your phone will be restored to the backup you chose. Be aware, you may lose some music and media and will have to transfer that on to the device.