Chosen Solution

I want to change the memory from 2x 512MB (total 1024MB) to 2x 1024MB (total 2048MB)

Wilfried Effer, one memory module is located on the bottom but another one can be accessed only if you remove the keyboard. The memory is under the keyboard but placed under the memory module socket cover. You can try and remove the battery and there may be one screw that secures this cover.