Voted a buzz on yahoo by mistake or added a vote to it? don’t just want to disappear from your profile but also remove 
any trace of what you just did accidentally? (including the message with your yahoo messenger id!) Its pretty much simple. Follow this to achieve this:
To change your vote, go to your My Activity page and look for the blue “Undo” button next to any story you buzzed up or buzzed down. We will then remove that story from your Recent Activity module. You cannot, however, edit or delete comments you make on Yahoo! Buzz.
So this way you can remove and change your vote to Yahoo! buzz.