What is DFU mode?
DFU (Device Firmware Update) mode is a state that allows you to put your iPhone to interface with iTunes, but does not load the latest version of iOS or bootloader onto it. That’s the main difference between DFU mode and recovery mode.
DFU mode allows you to change and choose the firmware you want to install onto your iPhone. For instance, you would use DFU mode if you want to install a previous version of iOS, jailbreak your iPhone or unlock your SIM. If standard recovery isn’t working for you to get your device back to working condition, DFU may help you out.
How to enter DFU mode
1. Plug your device into your computer and select your iPhone from the list of devices in iTunes.
2. Turn off the device.
3. Hold the power button for 3 seconds.
4. Press and hold the Home button while continuing to hold the Power button. Do this for 10 seconds.
5. Release the power button and continue holding the home button until you get a popup from iTunes that your device is recognized as being in recovery mode.
That’s it, you’re in DFU mode. This process works for the iPhone, iPod, and iPad so no matter what iOS device you’re using you can use this tutorial.
How to exit DFU mode
If you want to exit DFU mode, hold down the Sleep/Wake or Power button and the Home button at the same time for at least ten seconds, until the Apple logo appears.
Stuck in DFU Mode
If you get stuck in DFU mode and need to get out, just hold the power button and home button simultaneously until the Apple logo appears. (See also: How to Get Out of DFU Mode)