In a burst of energy in the past I installed twrp. But when I attempted to install 5.1 on my nexus 7 2012 by following the prompts, it dumped me into twrp with no information on how to proceed. Do I just hit the install button and find the update in my downloads folder and install that way?
I tried to flash the rom manually but failed miserably (ran into this page).
I decided to use the Nexus Root Toolkit (download here) to go back to stock Android 5.1 (losing everything on the device of course). That worked like a charm and re-rooting it afterwards was simple enough Rooting guide for 5.1.1.
In the past whenever a new Android version came out I had to flash back to stock Android to get the update and then re-root it. I'm sure some people manage to update without erasing everything...