You cannot upgrade to waterview. There are two choices for BWI concierge, Concierge and Deluxe Concierege. Deluxe Concierege has a larger room with a large sitting area. All other concierge rooms are standard concierge and can be anywhere on the concierge area. They do not offer standard and waterview rooms per se. The waterview rooms are by request only and those requests are not guaranteed
We did have a waterview room the last time we stayed on the concierge floor and it was wonderful so I suggest requesting it for your stay.
I believe that ALL of the Deluxe Concierge rooms are waterview in addition to being larger -- so you could upgrade to that if you needed that space.
Hope this helps
Michael