If you believe that upvoted or accepted answers to a question are wrong (or perhaps outdated, as the answers to the linked question are all over two years old), you can do several things:
- You can downvote them, an option you've already explored.
- You can comment on them, explaining why you believe them to be wrong or outdated. The user who wrote the answer will be automatically notified of your comment, and if convinced, will modify or remove their answers.
- You can go on Chat and attempt to convince people that these answers are wrong, and should be downvoted. Downvoting is the primary mechanism on StackExchange to differentiate wrong answers from right, and if those answers really are wrong, many on the site will be glad to improve the quality of answers provided, and downvote the incorrect answers.
- If you believe the accepted answer is wrong, you can comment on the original question, or on the wrong answer while @mentioning the original asker, urging him to reconsider and trying to explain why he's chosen a wrong answer.
- What you shouldn't do is Flag the answers for moderator attention. Moderators are not arbiters of correct or incorrect content. Moderators keep the site running, erase spam and abusive content, deal with malcontents, and in general (to quote the FAQ) "are there to deal with those exceptional conditions that could otherwise disrupt the community". They can't, and shouldn't erase content that is wrong. That is the community's job.
All of these actions should, of course, be taken in a polite and reasoned manner. Going around shouting "I'm right, you're wrong" won't win you any points in getting your message across. Our goal here is to have good answers to good questions. If you an just convince an answerer to fix his "almost true but slightly wrong or out of date" answer, especially to a two year old question, you'll probably be doing the site the biggest service.