Unplug your computer and remove the battery pack(s).
Notes on use
Adding memory
Sony Notebook User Guide
n N 90 
To install a memory module
1 Shut down your computer and disconnect all peripheral devices, such as your printer.
2
3 Wait until the computer cools down. Then turn your computer upside down and open the cover on the bottom by unscrewing the screw.
screw: turn counterclockwise
4 Remove the memory module from its packaging.
5 Install the memory module.