mobile

I have a used Unlocked XT1064 US Version with build 21.85.23 and I want to upgrade to lollipop but it does not work OTA. I am assuming it's because this phone has a custom build? (it seems to also have TWRP). So I believe have that I have to do stock recovery, but my question is which stock recovery firmware do I need to install that will allow me to get the latest updates OTA? and Is this the best way to upgrade?

Thank you