Read either one of these or both:
If you have problems of any kind with your account...And
HOWTO contact forum moderators/adminsThe admins do not really like to be bothered with this, but if you ask nicely they
might delete/close the username/account.
You can also simply change your password, to something random, that you won't remember, and just not use the account, but in the event that one day
you change your mind , all you need to do is use the "lost password" option
and get a new one.
If you really want to disable the account, change the e-mail address to a non existent e-mail, then there is no way to get a new password because you will not be able to use the "lost password" option with out a valid e-mail address.
Generally we do NOT delete or remove the posts, that could result in a topic that other members have replied to being incomplete and perhaps not make sense any more.