Back up your iPad to iCloud or a computer (Finder/iTunes).
Disconnect any accessories (except power if needed).
On the iPad, open Settings.
Tap General.
Tap Transfer or Reset iPad.
Tap Erase All Content and Settings.
Enter your passcode if prompted.
Enter your Apple ID password if prompted.
Confirm Erase and wait for the iPad to restart.
Set up the iPad again when the setup screen appears.