Age makes these plastic parts brittle. Even when you have the right tools and know what you're doing it can be a challenge taking these off without damage (especially the all plastic corner pieces). These panels are held on with "snap in" fasteners. I'm not sure the correct term, but I call them "Christmas trees". They are easy to install but can be a PITA to remove. For installation it's all about lining things up, then pounding the panel lightly with your fists in the key spots. Once the fasteners enter the holes in the sheet metal they grab on. Taking them back out requires outward force to be applied in specific locations. When prying these off, the closer you get to the fastener the better. There are
tools for this, but other things can work. Basically you slide the "pry bar" between the panel & the sheet metal, then move it along the periphery until it hits a fastener. When a fastener is located you pry outward. If you're too far away from the fastener the panel can crack or the fastener pocket (part of the panel) can tear/break out. Some panels overlap others, so in these cases take the top one off 1st. There are screws in some places, so check the panel carefully and always remove these 1st. Tim
PS: You may also want to go to Youtube and search for videos showing how it's done. I'm sure there's some videos there that will be very helpful.