Product Images Grid

Hi! I am using the free version of Virtue and am wondering if/how I can change the layout of my product images (on the product page). Some of the photos line up too close and I’d like to separate them, make more of a grid. For example, if you look at the 4 photos on the bottom/under the main photo (http://www.sleeneys.com/product/navy-and-emerald-necklace/), the spacing is not great. I’d like to change the layout to be more uniformed, perhaps 2 photos/line.
How can I change this, please?
Thank you so much for any advice that you may have!
My site is http://www.sleeneys.com.
Salina