I updated my Acer laptop recently. Much easier than a desktop upgrade. Just find out which little cover underneath hides RAM, take out the screw/s, slot the RAM in and put it back on. Mine was easier because the screw fell out of its own accord and the cover kept falling off anyway - perhaps it was a hint the it was desperate for more RAM.
My main concern was ro make sure it was compatible with Acer. I emailed Microwarehouse to check and they pointed me to the right product numbers. I'm sure other suppliers can be equally helpful.
I added 128 MB to the machines 64. It's made a incredible difference to how the machine runs.