To change the font size for your H1 and H2, just add into your custom.css "font-size: <you_value>px;" into the rule, I posted earlier. The same applies to the font family (read more about font family property at http://www.w3schools.com/cssref/pr_font_font-family.asp).
To be in control of CSS styles of your web-page elements, please learn to work with Firebug, for example, watching this tutorial at https://www.youtube.com/watch?v=3KdNRZS-uSg.