Oscommerce payment update problem

Having trouble when customers choose paypal as a method of payment. Orders are not getting properly updated. I believe this issue is happening because after our site directs a customer to paypal and they make payment they are not returned to our site they just remain on the paypal site after completing payment. The update is usually triggered when the customer is sent to the [login to view URL] page which after payment on paypal is made they should be automatically redirected back to the [login to view URL] page. I believe the paypal files on our site may need to be updated because the return path marked on the admin section under the paypal module is correct.