I would like to display 3 products per row instead of 4

I've got marketpress installed and need to change the page seen here: http://newsound.com.my/shop/

To show 3 products per row instead of 4, so that there isn't that big gap on each alternative row.

I can hard-code it but just need to know where this function appears in.

Also, on the /shop page inside Wordpress dashboard, I have other shortcodes on it, but they are not appearing on the /shop page, so not sure if this is contributing to the problem.

Thanks!

-William