heater box removal E250

I removed the side screws with no problem. The box is loose but there is one small phillips head screw way up on top center. What needs to be loosened or removed to get access to it?

all of the screws on the black plastic cover need to be removed, i know its a pain but a universal joint for your ratchet and a small extension will make it muck easer. send me an email at: [email protected] if you have anymore questions.