How-to Put iPhone into DFU Mode
DFU is stand for Device Firmware Update.
This tutorial will guide you how to put iPhone into DFU mode.
Please read these steps carefully before you decide to do it.
1. Open iTunes.
2. Connect the iPhone using its USB cable. Then, turn it off by holding the Sleep/Wake button (top right corner)
3. Press and hold down the Home and Sleep/Wake button on your iPhone together for 10 seconds.
4. After exactly 10 seconds, release the Sleep/Wake button without releasing the Home button until iTunes pops up a message telling you that it has detected an iPhone in recovery mode.
iTunes has detected an iPhone in recovery mode. You
must restore this iPhone before it can be used with
6. Then, you can release the Home button and your iPhone screen will display blank screen.
Video tutorial how to put iPhone into DFU mode: