Simply put - you can't directly yourself.
Only administrators have the ability to remove accounts. You can request any admin to remove your account, either by using the contact us form, or by contacting admin on site.

Why not?

Well we've experienced other sites ourselves, and we know how easy it is to abuse this self delete system. A member can join, hurl a load of abuse at people/profiles, write abusive messages in forum posts, then simply delete their account..
You will most likely know what we mean when we say the typical 'User no longer on site' status on profiles, and what it means.

Sadly, this is an easy way to abuse people and abuse the system.
So in order to protect YOU, members cannot simply delete their own accounts.