You got a CD with the Laptop. It should have all the detailed diagrams on it, mine turned out to be under the keyboard.
I have an earlier Advent and I could not see how to remove the keyboard. So I went back to PCW.
I had to buy a couple of other things anyway, and they were very quiet so they agreed to fit it for free!! The first stick he picked up turned out to be not what was written on the label of the sealed pack. The second stick was faulty. No charge and some good local craic at the same time!
These were both manufacturers problems, not PCW's, but had I tried to do either stick at home, I'd have been in trouble.
However, once I'd seen it done, doing it myself was a doddle, apart from the keyboard clip that didn't quite fit back properly, so now all is well.