Lets say one answer i saw is copied and pasted. how do i improve it? Is it okay to completely erase what the original author has written?
The best thing to do is flag the answer for plagiarism.
When you see an answer that contains entire paragraphs copied from other websites, your go-to option will be the Check for plagiarism flag.
This is true for copy/paste answers that have a link to the original source as well.
So, if you spot such an answer, flag it for plagiarism. Once we see the flag, we'll take a look an take imediate action - if the situation calls for it.
In the meantime, if you want to answer that respective question, do so in a separate answer.