Turn the device completely off.
Wait 10-15 seconds, press the Power button and the Volume Up button at the same time and hold them for 15 seconds to access the Android Recovery mode indicated by a red triangle with "No Command".
Release both buttons.
Press and hold the Power button and short press the Volume up to enter "System recovery" and release the Power button.
Navigate with Volume down to "wipe data/factory reset" and press Power to select (this will ask confirmation)
Volume down and press Power to select.
When complete, it will take you back to the System recovery page, select "Reboot System Now" to restore the device to factory default.