Welcome to Flyertalk! You can ask for a free upgrade at any hotel in the world. Whether you'll get one or not is anyone's guess. In Las Vegas, I have read about folks using the "$20 trick" by discreetly displaying a $20 bill to the front desk clerk and politely asking if complimentary upgrades are available. I have no personal experience at doing this so am unable to provide info concerning the success rate at various properties.