It depends on the laptop: sometimes there's a small opening at the bottom with one screw, sometimes you need to unscrew the whole bottom, and in other cases the memory is soldered onto the mainboard.
In your case, I assume there's a 1GB and a 2GB module. It's best to search your laptop type on Youtube for instructions on replacing memory, and find the right module on any memory website that allows you to search by laptop type.