Hi Ralph,
The first thing you should do is use Firebug which in built into the browser. Right click anywhere on your page and choose inspect element. From there you can drag over your page and it will highlight the the tag for what you want to change. You will see a dialog box on for firebug on the left. You can tinker with the properties of the CSS without effecting your site.
When you are ready and everything looks good, paste those changes into your styles.css file.
Don’t rely too much on the WordPress editor. Get a real IDE(integrated development environment) program such as: Net beans, Aptana Studio or text mate and cut and past your css there. When you make the changes, past it back into the WordPress editor. These IDE’s have version control so, if it is a failure you can return to the original CSS and copy and past it back into the WP editor.
If you want, send me the URL and I tell you the CSS that needs to be changed
