After booking a hotel, how can I get a free upgrade when I check in?

If the hotel has the room you reserved, it will basically not give guests a free room upgrade. Unless you find that you are not satisfied with the room after you check in, such as dirty or sanitary sheets, broken light bulbs, the room area looks too small, and the pictures don't match the real room. Ask the hotel to change rooms so that it is possible to upgrade the rooms for free. You can also directly tell the front desk whether you can upgrade your room for free when you check in. I'll give you five points. Try it. Good luck.