Just follow these easy steps:
- Turn the iDevice ON
- CONNECT it to the computer
- Make sure iTunes is open so you’ll know when it enters DFU mode
- HOLD the Power/Sleep-Wake button AND the home button for 10 seconds
- RELEASE only the Power/Sleep-Wake button and continue to hold the Home button
- WAIT until iTunes recognizes the phone in DFU Restore mode (in Windows a bubble pops up saying it recognized new hardware “DFU Mode” or something to that effect)
Another Way is to hear to the sound of the hardware Disconnect and Reconnect. When you hold power and home to reset, once you hear the USB disconnect sound leave the power button but keep holding the home until you hear another USB plugin sound. This is the easiest way to know that your phone is in DFU mode.