Yes, to remove the top part of the casing completely, you need to remove the carriage on this model (the bottom casing comes off quite easily by removing the four screws inside the rubber feet as you have no doubt found).  It is fairly straightforward to remove the carriage - you will see one large Pozidrive screw head in the carriage bed on either side - BUT you must disconnect and anchor the drawcord first !  You will find the drawcord attached to the front underside of the right hand carriage cheek.  It looks like a piece of clear fishing line.  Unhook it, and on no account let it go.  If you look along the front side of the carriage, you will see a two-pronged hook that has been built into the typewriter's frame as a temporary anchor.  Whist holding the end of the drawcord, move the carriage over to the left and park the drawcord on it's anchor.  You can now remove the two screws and lift the carriage straight up.  With the carriage out of the way, the top part of the casing will come off.

If I remember correctly, there is a secondary top casing that covers the area immediately behind the back of the carriage.  This is screwed to the bottom black base and you have to remove the carriage to access those screws.  Not a problem for a typewriter engineer of course, but the makers never reckoned on owners doing their own repairs and therefore didn't cater for it.