Different sizes for main product image and thumbs

I am attempting to use the full-size image that is uploaded as the main product image, with three thumbnails below. However, only the first of the three is shown full size on page load. When hovering over the thumbnails, a thumbnail-sized version is then displayed in the main image div, but the full size image is loaded into the div, it is just scaled down to fit the div size. If you the return to the first loaded image, it only shows at the small thumbnail size. I the problem is in the "ChangeImage" javascript in the image thumbnail links, but don't know where in the code to modify those values.

I believe I have set the correct sizes in the field options in multiple places. I have attempted to modify product->show but have only gotten the first image of the three to load at the full size.

Link to site: rockhartclothing . com/store/item/12-unplugged