In general, if you see another answer which is wrong, according to you, you can:
- Downvote it. You can downvote as soon as you have 125 of reputation.
- Leave a comment under the answer, explaining what is wrong about it according to you. The author will be notified of your comment. You can comment the other answer with 50 of reputation.
- As a last resort, if the answer is actually harmful (for example: unexpected loss of data, virus, phishing,...), and that's your only way to warn about it, you can flag it for moderator attention, and explain the issue. (Reputation needed: 15)
But in general, keep in mind that what is "accepted" is decided only by the one who asked the question. There are numerous cases of questions with popular answers, but the asker chose something else, most likely because it answered their own need. And that's ok like this. Votes are there to determine the better answers according to the community, in most cases.