If you look in the HTC One All Things Root Guide sticky post in this forum ( (International) One: All Things Root Guide
) you'll find links to threads for the firewater and rumrunner S-Off tools Scotty suggested. Just use one of those for S-Off. The same sticky thread also has a link to instructions for removing the tampered flag.
When you say you are having trouble updating, how are you trying to update? Also what ROM are you running and what recovery are you using?