You cannot delete that question. You can only delete a question while it is unanswered, or it has only one answer which has not been upvoted.
Where you can delete the question, it is reasonable at least to consider doing so. The system allows it. If it has an answer, you should bear in mind the effort taken in providing it. You may not feel any pang of conscience over a one-line answer; but you should seriously consider whether an answer with quite a lot of research behind it should simply be removed.
You should avoid editing a question which has already been answered, if your edit would invalidate the answers, or require them to be edited too. People have answered the question you asked, in good faith. If your edit does not invalidate the answers, it's reasonable to make it.
Note that questions should stand on their own as a coherent whole. You should not mark edits with the word "Edit" — the edit history is available to see previous versions. It shouldn't be necessary for readers to do their own mental editing ("Oh, I know the answer to that! Ah, the question's changed; now, which bit does that affect?")
Where it's not possible to change the question without invalidating answers, by all means ask a new question. Reference the original, and make it clear that the new question is different (so it doesn't get closed as a duplicate). I would recommend a structure such as
In my question [link], I asked X and answers explained Y and Z. However what I should have asked was A. Answers Y and Z don't answer that because B. What is the answer to A?