You would have to open up your orders_Results.php page and find the query that looks like this:
$query_WADAorders = "SELECT DISTINCT ps3_orders.* FROM ps3_orders LEFT OUTER JOIN ps3_orderdetails ON OrderID = DetailOrderID";
and modify it to look like this:
$query_WADAorders = "SELECT DISTINCT ps3_orders.* FROM ps3_orders LEFT OUTER JOIN ps3_orderdetails ON OrderID = DetailOrderID ORDER BY OrderID DESC";