[Q] How to revert back to being able to update via OTA? topic

Hey guys, I have an unlocked Nexus 9 and updating to 5.1 OTA isn't possible (as most of you probably already know). I have no idea what I am doing and only unlocked it because RootJunky had some automated program that basically did it for me. Now I'm stuck trying to figure out how to update manually...

My simple question is how do I revert back to a version (locked?) that will allow me to update via OTA and not have to deal with this going forward? Idiot-proof responses are most welcome.