I want to delete my own post as a question, but when I try, it says " you can't answer a question that has answers" . Any idea how to do it?
You can delete your own question, but not if it has been answered. Others have taken time and effort to provide an answer, and it would not be fair to deny them reputation for that contribution.
See Deleting my own question on MSO, the SE-wide meta, which provides more details.