You can not delete your account, even admins can not help you. This account deletion was stopped years ago and now you only can make a request to forum admin for changing your account username to something random, then lock it with security mode for you or you can abandon this account by  yourself.

theymos can change username to anonymous.
Another solution: change password, email to random, log out and abandon it.
or just abandon it.

You can proactively lock your account with the security question.
PSA: ACCOUNTS WILL BE LOCKED IF THE SECRET QUESTION IS USED TO RECOVER IT.