jborgman
You can edit in this file: /templates/gck_store/index.php
Look for this line of code:
<span id="s5_cart_icon" class="ion-ios7-cart ion-ios-cart"></span>
and change the class of ion icon to your desired icon.
Here is cheatsheet of icons used in template:
http://www.shape5.com/demo/images/general/ionicons/cheatsheet.html