1. Navigate to the iPhoneHeat website and scroll down until you see the header 'Download iREB RC3.' Click on the 'Windows' or 'MAC' download link, depending on your current operation system.
2. Start iTunes on your computer and put your iPhone in DFU mode. To put your device in DFU mode, connect your iPhone to your computer with your USB cord, hold the 'Power' and 'Home' button together for ten seconds, release the power button and continue holding the home button for ten seconds. Your iPhone should now be in DFU mode. If it is not, repeat the process.

3. Close iTunes and open the 'iREB RC3' file that you previously downloaded.
4. Select your device from the box that has appeared on your computer screen and wait until you see that your iPhone screen is red or white.
5. Reopen iTunes on the computer and find and click on your iPhone in the left sidebar of the iTunes program. If on a Windows computer, press and hold the 'Shift' key on your keyboard (Mac users press and hold the left 'Alt' button on the keyboard). With the button held down, click 'Restore' in the left sidebar in iTunes and then release the button.
6. Navigate to where your custom .ipsw is stored on your computer and select it. This should now allow iTunes to properly restore your iPhone to the newest Apple firmware.