Unambiguously incorrect information should be corrected, either by commenting and asking the originator to correct the content, assuming you have comment privileges (50 rep in beta); editing the post, if you have edit privileges (1000 rep in beta); or suggesting an edit if you don't.
If the information isn't unambiguously incorrect, it may be a matter of opinion or debate, then it becomes more difficult.
My suggestion would be to write a new answer, containing only correct information, from your perspective, along with the same conclusion, and leave a brief comment on the erroneous answer detailing the issues and pointing at your answer. It may be worthwhile including in your answer explanations of why another answer is wrong (especially if you can provide references), but please try to be nice and focus on the content, not on the individual.
While first post advantage may mean the the answer with incorrect information may start with more votes, over time it should attract fewer up votes and more down votes, with the opposite being the case for the more accurate answer.
Whatever you decide to do, you may well end up in a situation where a discussion in comments gets out of hand. Given that comments are only really intended to help improve questions and answers, and are not intended for extended discussions, if they do get out of hand, flag one of the comments for moderator attention and one of us can convert the whole discussion into a chat room.
- Given that Robotics has the potential to be life threatening, if a post contains information which you believe to be dangerous, you should also flag the post for moderators attention, along with any other steps you take above.