Erase all content and settings from iPad
When you delete data, it’s no longer accessible through the iPad interface, but it isn’t erased from iPad storage. To remove all of your content and settings from storage, erase iPad. For example, erase iPad before you sell it or give it away. If you want to save your content and settings, back up iPad before erasing it.
When iPad restarts with all content and settings erased, you have the option to set up iPad as new or restore it from a backup. (See Turn on and set up iPad.)