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.
(Here’s the video. She starts off by saying hotels prefer if you book with THEM instead of sites like Trivago or Expedia.)