related products

hi guys newbie to wordpress and html coding. am using mantra theme with woocommerce and have major problem with related products on a single product page. the thumbnail images are oversized and want 4 going across
as you can see from my website http://www.myshishafruits.com. as probably this has been covered before. am thick and stupid if some one could point me in the right direction to resolve my little problem

many thanks in advance
Enver