The DFU mode stands for Device Firmware Update and allows you to make several changes at the level of iOS on your iPhone device. When an Apple device is being put in the DFU mode, it means that the operating system did not boot yet and users are able to perform low-level modifications. People use the DFU mode when something works wrong on their devices. In the same time, the most common reason to use the DFU mode is to allow users to jailbreak their devices. I know that jailbreaking has become necessary and people hurry to jailbreak their devices as soon as possible. DFU mode serves for downgrading the firmware on your device when Apple does not give you access to perform this process.
This is how you enter your iPhone in the DFU mode in order to perform all those changes you hardly wait for.
Step 1: Connect iPhone to your computer and start iTunes application.
Step 2: Turn off your device by pressing and holding the Home button and the Power button in the same time for at least 10 seconds. This will turn off your device.
Step 3: While you keep on pressing the Home button, a small iTunes window will pop up telling you that an iPhone in a recovery mode has recently detected.
Step 4: When in the DFU mode, your device will have the screen all black. This means that the iPhone DFU mode is currently working. Any other sign such as the Apple logo or the iTunes application displayed on the screen means that you are in the Recovery mode instead of the DFU mode. The Recovery mode will not allow you to do all those changes you intend.
If you do not see the black screen, you should repeat all steps until you have success. To exit the DFU mode is simpler that entering it. All you have to do is to press and hold the Power button again for a couple of seconds until your device reboots in a normal state. However, if you performed any modification at the level of the operating system, all those changes will take place after you reboot. This tutorial was intended for iPhone use, but it works just fine for iPad or iPod Touch.