All the steps:
Step 1. Back up your device (really important)
Step 2.Download the latest iOS 6 firmware for your device from this website :
Step 3.Launch iTunes and put ur device in a DFU mode.
Step 4.Hold down the Alt/Option key (Shift in Windows) and click the Restore iPhone button.
step 5. ounce your iphone was restored you want to “restore from back up” and you want to select ur latest back up.