lay the unit flat on its screen, (I just laid mine on the bed). Push the stand flat against the computer and pop off the top cover of the stand. Remove the 3 screws that you can now see and the stand can be removed (option for wall mounting). Remove the plastic cover for the power cord and disconect anything you have plugged in to any sockets. (you don't have to unplug the video lead). I found it eaiest to pop the back cover from the right hand side by slipping my fingers inside towards the right and gently lifting, there are a series of plastic lugs holding the back cover in place all round the four sides, I used a small screwdriver to help ease these out. Once you have the back cover off you will see a squarish box in the centre. remove this tin plate by removing the 5 screws (there is one, lower than the other 4 down the left side).
You should now see the 2 empty slots for your memory. I used crucial.com's memory tool to identify the memory type (these were different for the z5761 and the z3101). I have photo's of the procedure but cannot work out how to get them onto my reply.
best of luck Scotstorm