wc-change-number-of-related-products.php

/**
 * Change number of related products output.
 */
function woo_related_products_limit() {
	global $product;

	$args['posts_per_page'] = 6;
	return $args;
}
/**
 * Display Columns and number of products.
 */
function wb_related_products_args( $args ) {
	$args['posts_per_page'] = 4; // 4 related products
	$args['columns']        = 2; // arranged in 2 columns
	return $args;
}
add_filter( 'woocommerce_output_related_products_args', 'wb_related_products_args', 20 );