You cannot delete it yourself, only one of the site Administrators can do that. Send one of them a message in their CC mail and they will take care of it for you.. If you choose to do this, and then decide you want to come back with this nickname or another one there is a $5 re-instate fee for all accounts. We don't let people delete and then make new accounts whenever they feel like, because it's really a lot of extra work for the admins, and so much harder to keep track of who is who.
The Admins are RoboOp, 1Still_waters and OnceFallen. Just send them a mail message. Usually they are quite busy, so this may take up to 24 hours before your account is deleted.