As a rule, if someone is honestly trying to answer a question but provides a wrong answer the best course of action is to downvote and/or leave a comment explaining why you believe the answer is wrong. First off, you may be wrong in thinking the answer is wrong, and secondly this gives the poster a chance to fix their answer and/or learn from their mistakes.
It's also a lot less harsh; if someone is answering a question then they're trying to help out. They may not be helpful at all, but outright deletion is a pretty strong response IMO, little more than "buzz off".
A (rare) exception to this are answers that are just spectacularly wrong. "What is two plus two?", "Your answer is bulldozer!" Arguably that's not really "wrong" because it just makes no sense.