A woman who used to work at a large hotel chain has a hack to get a free upgrade. First, you download the hotel's app, and then about 24 hours before check-in send them a message through the app.
Tell them you're excited about your visit and ask if it's possible to get a room with a view or one with a balcony. Stuff like that. They'll usually give you the upgrade for free because hotels want to make their "app people" happy.