Image Size

Hello All,
I’m working with MarketPress Lite and the Grid Layout Shortcode plugin (http://premium.wpmudev.org/forums/topic/3-free-add-ons-for-marketpress) and I’m having a bit of an issue with the images. My client would like for the thumbnails to be larger in the grid, but I’ve tried using the WordPress thumbnail settings and MarketPress presentation settings to change the image but nothing. Any help I would greatly appreciate, beating myself all day for this and I’m probably missing something stupid. The site can be seen at http://www.mcdonoughdesigns.com/clients/alaneweissman/products-2/

Thank you all so much in advance.

Mike