My understanding is the delete feature was removed during the site 'upgrade', a terrible idea for a forum such as this... If the delete account feature still does exist, I haven't been able to find it.
You could go through to all your old posts and edit each one to remove existing content and replace with nothing (........) to remove any/all content while you wait for a viable solution.
Hopefully Gypsy Nirvana can chime in... But no delete feature on an account is a serious security flaw for the site given the topic and different legal status all over the world.