Hello, @TFS,
I have checked the site link that you shared with us. The thumbnail images appear fine and when you choose an image from them it appears full as well as it appears in the thumbnail check the image: Under Private Content Area (1)
Now, The thing is the product images are coming from the WooCommerce plugin our theme has nothing to do with it. By default, WooCommerce has an option to set the size of images. navigate to the Dashboard >> XSTORE >> Theme Options >> WooCommerce >> Product images there you will be able to set the size of the images as per your need check the image: Under Private Content Area (2)
Regards 8Themes Team.