I'm not sure that you can delete a post, but you can go to the "edit" icon once you have posted and then delete the content. If you replace the text with "deleted thread" or something like that (as you did with your duplicate post, i see) then members will not open it. Maybe type "how do i delete a post" in the search box and see if theres another way.
That's pretty much what I have done. When you finish and hit submit it will show whatever you changed it to plus edited at such and such a time. You can go and delete everything and just leave something like