Ping Pong rooter -- now to unroot?

I used ping pong to root my phone, and now, I would like to be in a state that would allow me to upgrade to 5.1.1. I've only ever used root to use TI Backup and restore my google authenticator data. I don't believe i de-bloated at all, or done anything drastic to my /system partition.

Any instructions on the easiest/safest way of doing this? Preferably, without breaking knox.