There is no way to "Un-answer" right now. Strangely I've seen just two questions with two answers marked as "Accepted" - I don't know how that could happen, but it did. Anyway, the best you can do is to vote for the better answer. Or if the one you mistakenly accepted is totally wrong, you can ask the answerer if it's okay if you delete their answer and one of the editors on the forum can delete that answer completely so that it totally vanishes. And if you want to give the answerer 4 points instead of 2, you can BOTH vote for, and accept, their answer.
Best Answer