Enter DFU mode on iPhone / iPod Touch / iPad
Finding yourself in need of DFU mode for iPhone / iPod Touch / iPad do the following:
    1. Turn off iTunes.
    2. Connect iOS device to Mac / PC via native cable. (Look here how to connect properly).
    3. Power off iPhone / iPod Touch / iPad.
    4. Wait for 30 seconds.
    5. Press and hold for 3 seconds Sleep/Wake button.
    6. After 3 seconds, keeping hold on Sleep/Wake press Home button for 10 seconds.
    7. After 10 (exactly) seconds, keeping hold on Home button release Sleep/Wake one, after that keep pressing Home for about 15 seconds more. (Screen should remain black, if you see anything but a blank screen, you got the timing wrong. By repeating above stepsyou must try again until you get it right ).
    8. When “new device found” message appear on computer screen your iPhone / iPod Touch is in DFU mode.
Procced with advice on how to quit DFU mode