Catalog image size not changing

Hi, I am having this problem and looked all day for a solution, but nothing concrete.

I tried to change the size of the catalog image to a custom,smaller one with no effect. I have tried the Regenerate Thumbnails plugin, even edited the image for a size as the catalog one, but still nothing.

I even replaced some width sizes in code, as some said on other forums, but no effect. What exactly should I change in code and where? Some say its in woocommerce.css, others in theme’s style.css. The guy who handles the customer support of the theme is busy, so I must take care of this on my own 🙂

P.S. I also installed WooCommerce Product Archive Customiser so I can get 4 collumns instead of 3, like the theme’s original, if this has any implication.