The first thing you have is the iTunes program on a computer, either Apple or Windows. It is important that you have the latest version before starting the process to restore your iPhone with the backup.
Then connect your phone to your computer. Depending on how you have configured, iTunes opens automatically detect that the device is connected to your computer or you manually have to go to open the program.
Already in the iTunes interface, you must go to File, Devices and then click Restore Backup, which is the option that will allow you to make your goal. In the event that your version of iTunes is 10.7 or earlier, you must place on the device with the mouse right button and dial, there access Restore backup.
It is important that you consider the following information before restoring a backup to iTunes on iPhone: Unable to install backup devices with iOS versions older than those of that with which the backup was performed .
For example, imagine you have an iPhone 5 in which you installed the iOS 8.1.1 version and then you made a backup in iTunes. Now, you want to restore the backup on an iPhone 6 comes standard with the iOS version 8.0.
You can not do that, you have to start the phone without the backup and update it. Already with the latest operating system, yes you can perform the operation.
As you can see, restore a backup to iTunes iPhone is simple. So do not be lazy and make your backups regularly to ensure they do not lose data.