woocommerce gallery view custom image size

hi,

when i pick 3 products in a row from woocommerce settings the images look so big as gallery thumbnails. and when i pick 4 products in a row the thumbnails look so small. for example i want 4 products in a row but i want them look bigger

how can i customize gallery thumbnail sizes? if you want to take a look at how my gallery view looks like HERE

thanks