I have an accept rate of 0, but I don't see any button in my view of Stack Overflow that would allow me to accept an answer.
To the left of each answer, there should be a large outline of a check symbol. Logged in as the person who posted the question, you can click on that check, and it will turn green. That indicates that you have accepted the answer to which the check mark pertains.
Clicking on another transparent check will undo your previous acceptance and reassign it.