Performing a factory reset may take some time, so make sure that you plug your device in to a power source before you start. If your phone becomes unresponsive at any point during these steps, you can restart it by holding down the Power button for several seconds.
If your phone is on, turn it off.
Press and hold the Volume Down and Volume Up buttons, and then press and hold the Power button at the same time until the phone turns on. You'll see the word "Start" with an arrow around it.
Press the Volume Down button twice to highlight "Recovery."
Press the Power button to start Recovery mode. You'll see an image of an Android robot with a red exclamation mark and the words "No command."
While holding the Power button, press and release the Volume Up button once.
Press the Volume Down button twice to highlight "wipe data/factory reset" and press the Power button to select it.
Press the Volume Down button seven times to highlight "Yes - erase all user data" and press the Power button to select it.
After the reset is complete, press the Power button to select the option to reboot your device.