Why do you want to delete your account/threads? To answer your question, you can't delete it. If you really want you can simply ignore it and no longer sign in. As for threads, threads are only deleted when they have spam/advertising/vulgar in nature.
Just a-wondering. Last forum I was apart of I could delete my threads, posts and account with a click of the mouse. Anyway. Thankyou for the help, helply-helper person. Guten Abend.