No. Once you have submitted a question, take, opinion, or comment, you cannot edit or delete it. We do not remove posts per user request. If it doesn't violate any site rules, we won't remove it. Please carefully consider what you post before clicking Submit so as to avoid 'post regret'.
However, you can update your question using the Update link on your question page. You can change it to or from anonymous by checking or unchecking the Anonymous box from the post. You can also Disavow the question, which makes the question Anonymous and you'll no longer receive notifications. To Disavow, hover your mouse over the broken link symbol next to the question title on your question list page and click Yes. Please remember, you cannot reclaim the question after it's been disavowed.
You can't delete a post on GaG. Only admin can ultimately decide to do so, and that's usually under circumstances wherein your post violates one or more of the site's rules.
What you CAN do are either go back and make your Opinion or Question Anonymous, and you can also utilize the Disavow feature. The latter option essentially makes your Question (not opinion) anonymous AND it stops you from receiving any notifications should there be any activity on that Question.
You mean one of your own? If it's a question then after 24 hours you can "disconnect" the question from being yours. Meaning you quit getting notifications and it doesn't show up in your questions. It post as a anon.
If it's a comment or opinion the only way is for it to be so bad that it's deleted by admin or possibly if you just ask a admin to delete it.