How to remove door panels?

You don't need a trim set. You can just get something thin and flat, like a paint scrapper. If you lay down and look along the bottom edge or side of the panel, carefully pull the panel out a hair and you will see the metal pins that push into the small holes in the door. Then when you feel one, slip a couple fingers in and around the pin and pull it out. Once one pops out, the rest will be easy to pop out.