Pull up on the corner pieces of the cover assembly to remove them.
Remove the horizontal lower and upper plates of the baseboard water heater by jiggling gently to release them from the hooks. Don’t pull sharply or you risk warping the thin metal. Instead, peer inside to see how the hooks are holding them,then detach the plates carefully.
Remove the screws attaching the backing plate to the wall, using either a Phillips or flat-head screwdriver as required.
Separate the backing plate from the wall and pull it away from the pipe and metal fins. The pipe and fins will be far enough from the wall for you to remove and replace the drywall.