Mouseover is a function available on HTML. Since this is a HTML builder, you can implement the simplest code possible to have the desired effect. Switch to the code view when you are building the website then add the following code for your elements:
<img onmouseover="bigImg(this)" onmouseout="normalImg(this)" border="0" src="Image.EXTENSION" alt="IMAGE" width="32" height="32">
You can tweak the resolution for the thumbnail and big image. It's necessary to use the function for everything to work properly.