Connect your iPhone to your computer. Open iTunes. Turn off your iPhone. Press and hold the Power button for about 3 seconds. Don’t release the Power button. Press and hold the Home button for about 10 seconds. (If you see the Apple logo, you press too long and you need to start anew) Release the Power button but keep holding the Home button for about 5 seconds. (If you see the Plug into iTunes screen, you press too long and you need to start anew) If the screen still stays black, you enter the DFU mode successfully.