Change Woocommerce Products per Page.

 Add this to the Child Theme Functions.php . 

add_action( 'after_setup_theme', 'change_parent_products_per_page', 10 );
 
function change_parent_products_per_page() {
   //chnge how many products are displayed per page    
    add_filter( 'loop_shop_per_page', create_function( '$cols', 'return 24;' ), 20 );
}

Best.