First off either make a note of your ALL of your desired current router settings or alternatively you might already have backed up a "good" running configuration of your router to your computer without all of the spurious user names that you want rid of.....
Having satisfied yourself as to which is best for you, then you can either restore your earlier back up (without the spurious user names) or whilst the router is powered up put a pencil or a similar narrow pointed nail like device into the little hole at the rear of the router and hold it gently in position for 5 seconds or so; that sets the router back to default. Defaulting it has some virtues in that you get a factory set up, the bad news is that you then have to set it up again with all of the settings that you destroyed by defaulting it!
After you have the router up and running make a configuration back up (easy to do) and keep it somewhere in one or more of your PC(s).
Valuable information resources can be found
here
Good luck
Go with the flow
xoff