Accepting answers is 100% the original question poster's opinion. We don't mess with that. We also can't unaccept an answer or force answer acceptance. The community can't really, either. (Evidence: my answer on "Easiest way to setup Ubuntu as a VPN server, the +500 bounty I was awarded on it by posting a working answer long after an accepted answer was there, and the fact the 'accepted' answer has been flagged to be removed multiple times with all of those times being declined, from what I can tell)
We also tend to try and avoid deleting accepted answers, whether they're wrong or not. I'd add a blurb to your post as an edit that "Note: the other answer here is better, consider using that one instead" and link to it. I've had to do this at times myself in the past.
Sorry, but I'm not comfortable sniping an answer simply because one is 'better' whether yours or not. Especially when it's already accepted - we try and leave that to the 'community'. (There's only a few cases where I'd torch an answer that's already accepted, and that's usually only if the now-accepted answer is going to cause seriously horrible things or now links to malware or something)