Please make sure you do not have any more active games, and you are not playing in any mini-tournaments, and you have withdrawn from all other competitions (League, Ladder, etc.) — if you'd like to cancel your account on GameKnot please use the following link: permanently close account
Please note that this action is permanent and cannot be undone, and that your user name cannot be used again (i.e. you won't be able open a new account with the same user name later on), so please make absolutely sure that's what you want. It would be much more advisable to keep your account open, just in case you return to playing chess in the future (you never know!).