This is how I got into the TC15
Having removed the screw you need press down gently on the cover and then slide it to the rear by just under 1cm. It can then be lifted clear.
The memory SODIMM and a mPCIe socket are on the rear of the board. To get to these you need to remove the board from the case.
Remove the four chrome screws that are (approximately) in the four corners of the motherboard.
The next stage I originally found to be a little tricky. I find it easier now, possibly because
I broke something. Essentially you just lift the rear (back panel) of the board and slide the board out
of the case. Initially I found this to be difficult as something near the DVI socket was obstructing
this and preventing me raising the back panel. However I tried to manipulate things it just wouldn't
fall apart. Eventually brute force and ignorance won the day.
You may want to try to see how you can encourage this point to release before resorting to force.
Reassembly is just a matter of reversing the process. A good way of starting is to make
sure that the mike/earphone sockets are properly located in the holes in the front panel
as you slide the motherboard back into the case.