Ask in Settings → Privacy. Your account, your email address, your profile and anything else that identifies you are removed.
🚨 Your posts are a separate question, and usually they stay. A conversation is not only yours: deleting your half of a three-year-old discussion leaves other people's replies answering nothing. The usual arrangement is that posts remain with the name removed.
Whoever runs the site decides that policy and can tell you what theirs is. If you need something specific taken down, ask before deleting the account — afterwards there is no way to reach you about it.