Check that the name you wish to use isn't in use here, and then send a PM to Anandtech Moderator asking nicely for a name change 🙂
If you come back and find you can't log in (or if you stay logged in and it says something about cookies expired) then they have changed your name for you 😉
If they do it, it won't be instant, but they are normally pretty good at doing name change requests 🙂
Garry