The theme comes with full support to google fonts. If you wish to modify the fonts you can do so by going in Theme Options -> Typography, here you'll have the ability to set 2 different fonts for normal paragraph texts and headings.
It's important that you set the url like showed into the example in the options panel. The url of the fonts must be without the http protocol in front of it, WordPress will handle the protocol.
To pick a new font, browse the google fonts catalog here http://www.google.com/fonts, select the font and then copy and paste the url from the google font page (example image below here) into the appropriate field of the theme options panel.
Once you're done, make sure you set the font name into the appropriate field. The video tutorial below here refers to another ThemesDepot's theme. However the instructions and options of the theme options panel are the same.