MarketPress products page thumbnail size to large and pixelated

HI, I’m running Marketpress lite on Pinboard and on the Products page that the plugin creates the thumbnail window I believe is to large and is not shrinking down to match the image. The image box always remains the same size no matter what size and resolution of the image and thumbnails that go into his area become to pixelated to see. Is there a way to re-size the image box for product thumbnails or this type?

Thank you.