Improving an answer on Wikianswers is simple. Just click the green "Improve this answer" button and edit the answer so it is better. You can also click the "Edit this page" link.
For commonly asked but unwanted questions, redirect the page to Why was my question redirected here. For example, pages like what? aren't going to contain meaningful content, but get asked again and again.
For answers that you know need improvement, but you aren't sure you have the correct answer or you're just too lazy to improve, you can list those for improvement using {{improve|reason for needing improvement}} — just type that on the page above the content.
Some common reasons for answers needing improvement:
Questions that are marked for improvement {{improve}} go to the "Candidates for Improvement " category. When you "answer" the question you can mark it as a candidate for improvement.
Any user is capable of marking an answer for improvement .
If the answer is too insulting you can also consider replacing the entire answer with the {{improve}} tag.