This has probably already been asked before. How do I delete a thread I started?
From the guidelines:Why can't we be able to delete our threads? I want to delete all mines.
Additionally, members are allowed to delete posts they have made so long as it is not the first post in a thread (i.e. a new thread started by the member). When the first post of a thread is deleted, the thread itself is deleted along with all the posts in it. This rule exists because threads can contain posts from many members and it would be unfair and harmful to the community if individual members had the ability to remove the posts of other members (potentially hundreds of posts in a single discussion thread).