mobile

I have an AT&T HTC One M8 thats fully rooted. S-Off, unlocked boot loader and rooted stock sense ROM. Lately its been causing more trouble than its worth (just being slow) and I want to fully unroot it and turn it back to a factory state. Its still android 4.2.2 and I want to unroot it so I can get the lollipop update. I've tried a few times before and when I get to the point where I'm supposed to flash something in recovery I get the "md5 mismatch" error. All I want is for my phone to be unrooted and back to normal. If anyone can help, thanks!

And I also paid for s-off on this phone so if I could keep that without any trouble, I'd like to know how to do that too.