If you edit "theme-globals.php" in the theme folder you will see the following code on line 88:
$s5_loop_tags['before_content'] = '<div style="clear:both;height: 15px;"></div><div class="s5_contentwrapper"><div><!--%thumb_block%-->';
Just change the `height: 15px` to whatever height you would prefer.
The theme-globals file defines a lot of the content structure. It is also a file that is designed to be excluded from updates to the framework; any changes you make will be preserved, even after installing any patches that I release in the future.