trailer interior question

[2gofaster]

Anyone know how to get these upper corner pieces out of a Haulmark and other trailers? Is it as simple as pushing in the middle like a mother in order to get a screwdriver under the lower side and start popping it out of the channel? I need to replace the romex to the AC and at a minimum I need to get into that space. Worst case I'm going to have to pull it out and pull the lower channel so I can get a wall panel out. Which means I also have to pull the light fixtures out. Because of the wires going to those light fixtures, which runs through a hole in these corner pieces, I also can't just slide them down.