WooCommerce - change number of products displayed per page

functions.php

add_filter( 'loop_shop_per_page', 'new_loop_shop_per_page', 20 );

function new_loop_shop_per_page( $cols ) {
  // $cols contains the current number of products per page based on the value stored on Options -> Reading
  // Return the number of products you wanna show per page.
  $cols = 9;
  return $cols;
}

@PaolaGress Maybe you should look in the source code of your theme to check if there is a hard-coded value.
As far as I remember, the code snippet form above was meant to be put inside functions.php in a child theme of your main theme. https://developer.wordpress.org/themes/advanced-topics/child-themes/
Hope this helps!

add_action( 'woocommerce_product_query', 'woocommerce_product_query' );
function woocommerce_product_query( $q ) {
    if ( $q->is_main_query() && ( $q->get( 'wc_query' ) === 'product_query' ) ) {
        $q->set( 'posts_per_page', '5' );
    }
}