"popular features" is using a rokcandy macro in the title of the module. It also has module class suffixes added in the module and finally there is a joomla modules override to add the "rt-bubble" class in the module rendered output (/templates/rt_chapelco/html/modules.php).
If you want to use your own images for icons then you could restyle one of the existing classes (e.g. the icon-star) or you could instead create your own class (I'd suggest giving it a name of that begins with "icon-" and then adding your own custom CSS for that class.
.icon-xxxx {
content: url("youriconimageurlgoeshere");
}
If you do all your development locally then it is going to be much harder for us to assist you - I would suggest that you get your site on the net if your require further assistance.
Regards, Mark.