Removing the top panel of the main body is performed by removing the screws from underneath. There are a set of four which are easily accessible, but this doesn't free the top panel . To get this free, you need to use a long reach Phillips screwdriver with a magnetic head.
The image above shows the hole which connect through to the screws which hold the top panel in place. The long reach is required as they are quite a distance within the unit, and a magnetic head is required to ensure you can remove (and eventually return) them.
Once these screws are removed, the top panel is easy to take off, and the inner workings are revealed.