IF your question on Yahoo Answers has no answers yet, you can just go into your question and select Edit>Delete. (make sure your mobile device is in desktop mode, if using a mobile)
IF your question on Yahoo Answers DOES have ANY answers, it cannot be deleted. The only way to get it removed if it has answers from others, from that point on, is to have enough accounts report it as a violation, so the system removes it from the display. You cannot edit or change the info you posted, either. All you can do is add updates to clarify it, or make yourself Anonymous (Edit>Post as Anonymous) to hide your identity.
This is probably the single most asked question, over time, in the Yahoo Answers subcategory. You can save points and time in the future, by doing a search at the top of the page (type in your question or keywords and press "Search Answers"), to see if the question you have has already been asked/answered. How to delete questions has been asked/answered literally thousands of times since the site was created.