Font and size changing, please help!

Hi all, Im using Simple Catch to build my own site www.bluecavedivers.com. I have to say that’s the one I like very much, sharp and clean. As I am a such layman to Wordpress, so I need to try many things to carry out everything I like. I would like change the fonts and sizes of the heading which is a 2-rows array besides to the square logo, however I do not know anything about CSS and codes, that’s why I am disturbing and asking help. Thank you so much for your times and looking forward your replies!