Turn off your iPhone then connect to iTunes. It will tell you it cannot sync because the iPhone is locked with a passcode, press cancel. On the left of iTunes you will see Devices and your iPhone should appear there. Right click on your IPhone under Devices and select restore from backup, a message box will appear indicating when your last backed up, click on restore.
It should be noted that it can only restore from a back up if you have previously backed up your iPhone to iTunes. Any data placed on your iPhone after the last back up will be lost.