How to flash kitkat on shield tablet?

Can anybody tell me how i can flash my shield tablet to an early firmware/os version? i recently rma-d my tablet, and apparently i can keep the old one, but it has a kill switch, and will be dead if i activate the new one. id like to sell this tablet since theres nothing wrong with it, no batter troubles, and i can always replace the battery just to make sure, and if i outline the risks im not liable. anyway id just like to downgrade so the kill switch isnt there anymore, and have no idea how, ive never even rooted since its always would have voided the warranty. apparently theres a factory image reset file that im supposed to use, but its gone from nvidias site.

Follow this guide:

Make sure to read it well and take your time.