If it is a pm...you can't delete it.
If it is a post on a thread, you can't delete it, but you can click on the edit button at the bottom of the post and let the DISigner know that you no longer need help (or post whatever you think is appropriate).
If it is a thread you can't delete it, but you can click on the "edit" button then click on the "go advanced" and change the title and body of the post. For an entire thread...you may be able to send Penny (Chaoscent) a pm and ask her to delete the thread as she is a moderator for our forum. Hope that helps.