Most people don't delete queries once they have their answer - it usually sits there to help out people in the future looking for the same answer, IF they can be bothered to use Google and search for it.
Leave it there, help someone else out.
You can get a post deleted by clicking on the down arrow next to the three dots to the right of the Report button, it will ask for a reason though.
You cannot delete it or a thread directly as only moderators or Admin can do that
Usually what is put on the forum stays on the forum.