To do a factory data reset, follow these steps:
If your phone is on, turn it off.
Press and hold the Volume up button and the Power button at the same time until the device turns on.
Press the Volume down button to select "Recovery mode." If you need to navigate to the "Recovery mode" option, use the Volume up button to move the arrow and the Volume down button to select it.
You’ll see an image of an Android robot with a red exclamation mark and the words "No command."
While holding down the Power button, press the Volume up button and release it.
Use the volume buttons to scroll to "wipe data/factory reset" and press the Power button to select it.
Scroll down to "Yes - erase all user data" and press the Power button to select it.
are you sure you get it right?
choose factory data reset when you are in recovery mode push power button for 10 - 15 seconds to shut it off totally. then doo the recovery mode factory data reset(power button+volume button)