If you flag the question and include the reason you wish to withdraw it in your flag, the moderation team will consider removing the question. When a question is removed, all the responses it received disappear too—the results of the time and effort that other jellies put into giving you a good answer, a rousing debate, or a nice conversation suddenly vanishes. It’s not fair or respectful to those who put effort and good faith into answering to remove questions left and right.
Unless, of course, you are still in the first few minutes of asking it. Then you can edit it like others suggest.