How to get rid of Optimalratepro?

I have OptimalRatePro malware on my new imac and trying to get rid of this. Tried downloading Anti-virus software but it doesn't seem to detect it. I cannot just delete it from the extensions in my Chrome. It is basically making my search engine default to Yahoo no matter what I do. I'm not so worried about that as much as the possibility my data may be stolen. Can anyone help get rid of this malware?

[Re-Titled by Moderator]