WooCommerce – Change number of displayed upsells on product pages

add_filter( 'woocommerce_upsell_display_args', 'custom_woocommerce_upsell_display_args' );

function custom_woocommerce_upsell_display_args( $args ) {
  $args['posts_per_page'] = 5; // Change this number
  $args['columns']        = 5; // This is the number shown per row.
  return $args;
}