If you booked with a travel agent, it is always worth going back to them and they will contact the tour operator for you.If you booked online, it is still worthwhile e-mailing the operator. They do tend to be very helpful. Did your brochure advertise rooms with a sea view at a supplement? If so, and there are rooms like this still available, i would imagine though that as well as paying the extra for the room, you will also probably have to pay an admin fee which can be around £20- £25 per booking so be warned!!
I used to have a friendly travel agent and once when i had to make a late change to a booking, she managed to get the admin fee waived. Don't hold your breath though!
Good luck and let us know how you get on.
John