If your tablet is on, turn it off.
Press & hold the Volume Down button, then press & hold the Power button simultaneously until the tablet turns on. You'll see the word "Start" with an arrow drawn around it.
Press the Volume Down button twice to higlight Recovery mode.
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 down the Power button, press the Volume Up button.
Use the volume buttons to scroll to "wipe data/factory reset," then press the Power button to select it.
Scroll down to "Yes - erase all user data," then press the Power button to select it.
Note: If your tablet becomes unresponsive at any point during the steps above, you can restart it by holding down the Power button for several seconds.