There is no option for a user to delete their own thread. Once you've reached a certain number of posts, you are able to delete posts via the Edit Post option, but you cannot delete a thread. If you no longer need a thread then use the Report Post option to send a message to the mods, who can delete it for you. That said, if you have found a solution to your own problem then it is preferred that you add a new post containing the solution. That way, you may help someone else with a similar problem in the future.