Are you talking about an editor? If so, it would have made a *.css file. You can change your rules in there. if it hasn't, then the rules will be in the <HEAD> of your document.
To see ehat file the CSS is coming from, look in the head for <LINK REL="stylesheet" href="yoursheet.css" type="text/css">
Then you will know exactly what it has called it. Dean Owen