(After following the first part of the tutorial) Still in Templates, find Forum Bit Templates -> forumbit_depth2_forum (Do the same for forumbit_depth2_cat) and replace:
The only parts of this you'll want to change are the numbers and the icons (There's some info at the end of this post about that). To find the number of a forum, when editing one in Forum Management, just look in the address bar for &fid=, whatever number follows that is the number to use in the CSS selector.
Finding New Icons If you're using Google Chrome you can go here http://fortawesome.github.io/Font-Awesome/icons/ and right click > inspect element. Then expand the <i> tag and click the ::before element, which should show the icon in the right sidebar.