I would look at the Kentico REST API. When you configure your rest service and it is pretty simple
GET - will give you all the orders:
http://localhost/K8/REST/ecommerce.order/
SET status for oder #10 just do PUT
http://localhost/K8/REST/ecommerce.order/10
<COM_Order>
<OrderStatusID>8</OrderStatusID>
</COM_Order>
It is all pretty well described in Managing objects using REST