You can adjust this in the block of code you add to your header:
<!-- Start of the headers for CoffeeCup Web Form Builder -->
<link rel="stylesheet" href="./c/colorbox/colorbox.css" />
<script src="./c/common/libs_js/jquery-1.4.4.min.js"></script>
<script src="./c/colorbox/jquery.colorbox.js"></script>
<script>
var $fb_pop = jQuery.noConflict();
$fb_pop(document).ready(function(){
$fb_pop(".fb_iframe").colorbox({iframe:true, innerWidth:"672px", height:"80%", maxHeight:"811px", fixed:true });
});
</script>
<!-- End of the headers for CoffeeCup Web Form Builder -->
Just change this part:
$fb_pop(".fb_iframe").colorbox({iframe:true, innerWidth:"672px", height:"80%", maxHeight:"811px", fixed:true });