I think that there is only one semi-strict rule about editing across Stack Exchange, and that is "don't start an edit war with the original author." Since you're the OA, that obviously doesn't apply here.
There's some other guidance in the above link, but it's kind of dated, and not even the site owners really agree on a single universally-applicable methodology. There are basically three schools of thought which I suspect will always exist in isolation:
The everyman school: Don't edit anything unless it's totally safe, like a barely readable post that's been downvoted.
The Jeff school: Only edit to fix minor errors like spelling, grammar, and formatting.
The Joel school: Edit whatever you want, whenever you want, however you want, as long as it substantially improves the question/answer (and therefore makes the internet a better place).
Personally, I'm a stalwart supporter of the Joel school. Excepting extreme cases like the bait-and-switch, which loosely fall into the general "don't be a jerk" guidance, you shouldn't be afraid to perform major reconstructive surgery on any post, even if it's somebody else's.
If you own it, it's practically your responsibility to improve it, especially if it's highly-voted/accepted and even if it means a total rewrite. This isn't just armchair speculation from me, trying to convince you to rewrite your answer; I practice what I preach. I don't have that many answers on P.SE to demonstrate, but I've done this frequently on my home turf after realizing that one of my earlier answers was... well, crap.
It makes no sense to tell people not to change the content of their answers if the original content is wrong, misleading, incomplete, or simply not the best that it could be. The whole aim of this crowdsourcing exercise is deliver the best possible answers we can.
Editing unfreezes voting, so if the people who voted for the previous answer no longer like the "new" answer, they are free to rescind their votes. Which means that you might lose reputation, but (a) I doubt that'll happen if the edit is truly an improvement, and (b) if you're really worried about that then you might be posting for the wrong reasons.