Technique: iPhone 4 / 4S / 5 / 5S / 5c / 6 / 6S - how to flash from DFU mode. Password recovery.
Entering DFU Mode (Official Instructions)
1. Plug your device into your computer. 2. Turn off the device. 3. Hold the Power button for 3 seconds. 4. Hold the Home button without releasing the Power button for 10 seconds. 5. Release the Power Button but keep holding the Home button. 6. Keep holding the Home button until you are alerted by iTunes saying that it has detected a device in Recovery Mode
Make sure the device screen is blank and no logos are present. Same operation you can use for all other models of iPhone.
Open iTunes. The iPhone must be connected to the PC and powered OFF.
ATTENTION, ATTENTION !!!
You will lose all your data. Be sure that you have backup.
Entering DFU mode.
Instruction you can read at the description.
iTunes has detected an iPhone in recovery mode.
Select "Restore iPhone" and iTunes will download and install the latest firmware for you phone.