I opened the lid by flipping two small catches and this is what I found:
In the foreground, you can see a crossmember which stiffens the case. This will be the first thing to be removed. It must be kept for future use though.
In the back, you can see the PCI slots with one card. That is easy enough to remove.
To the right of the PCI slots, you can see the processor units. There are two here and there is room for two more. They come out with the release of a few catches.
Below the crossmember, you can see the fans that cool the processor modules. These can be unclipped and removed.
In the foreground at the left, below the crossmember is the fan that cools the drive bays. That also lifts away now.
Now we come to the tricky part. The backplane, with the blue plastic cage attached must be unscrewed from the base of the case but it is not so easy. At the top of the picture, in the corner, you can just see part of the metal bracket that houses the connectors for the incoming mains power. You have to undo the mounting screw and then jiggle it about inwards and then upwards to get it to come clear. One of the mounting screws for the backplane is hidden beneath this so you have to get it out.
Once you have done that, the back half of the case is empty.
(More to follow)