Just click "delete". The tooltip says "vote to delete", since it technically is a vote, but since you're the author of the answer your delete vote is binding.
The only exception is if the answer has been accepted by the question's author.
Note that posts on Stack Exchange are soft-deleted - your own deleted answers will still be visible to you and users with at least 10,000 rep (and moderators). Deleted answers have a red background, a note on them saying that they've been deleted. They cannot be voted on, and they don't affect your reputation unless they're over 60 days old and have a score of at least 3.