<p>While the canonical "StackExchange/StackOverflow" approach seems to be to allow downvotes, edits and new answers and hope the new good ones eventually float to the top, I think that in practice the best thing to do is make a <em>new</em> question (if possible, worded to be in as canonical form as possible), and enure it gets at least one decent answer. Then close the old one as a duplicate of the new one, adding a note that the answers there are now outdated and better answers are at the new one. </p>

<p>This should get to a desirable outcome faster. </p>

<p>Edit: I agree with amoeba that the standard approach should still be used if there's a reasonable chance of that working. </p>
