Always ask for a free upgrade to your room.

Hotels are looking to get to full capacity.  If they already have you there in a cheaper room, when someone calls to make a reservation, they may not want to spend the money on a more expensive one.  The hotel will lose that business.  If they move you up to a better room, that frees up the less expensive room.  Now the hotel can book your cheaper one, and make more money.  WIN/WIN