Navigate to wp-content/themes/theme_name/fw/core/core.lists.php file. You will see the list of all fonts available:

In order to add the new font, duplicate one of the default font strings, for example

'Advent Pro' => array('family'=>'sans-serif') ,

and replace the name of the font with the font you would like to apply. Save the file. 

With that done, go to Theme Options - Fonts and Colors and you will see this font in the selection list.