These are optional theme settings that you can set when declaring WooCommerce support.

function mytheme_add_woocommerce_support() {
    add_theme_support( 'woocommerce', array(
        'thumbnail_image_width' => 150,
        'single_image_width'    => 300,

        'product_grid'          => array(
            'default_rows'    => 3,
            'min_rows'        => 2,
            'max_rows'        => 8,
            'default_columns' => 4,
            'min_columns'     => 2,
            'max_columns'     => 5,
        ),
    ) );
}

add_action( 'after_setup_theme', 'mytheme_add_woocommerce_support' );