Thumbnail size

Hi,
I’m losing my mind over changing the size of product thumbnails for here: http://www.hobkey.com/keyak/.

I set the product thumbnails (Catalog/Image Options) to 300px and regenerated thumbnails.

I tried to edit the content-product.php to show thumbnails with:
the_post_thumbnail();.
But it’s still the same.

I changed the related product image size, but the sign “Sale” is in the same place: http://www.hobkey.com/shop-2/orange/.

Where in the code I have to look to solve this problem?

Thank you, Marin

http://wordpress.org/extend/plugins/woocommerce/