If you are in the UK look at different supplier sites and look for DDR2 Note book memory of the type you require (DDR2 PC2-640), I did a quick look at Overclockers UK and Scan and both have this type of memory and in different sizes. Normally on a lap top you have to unscrew and small panel on the bottom to access the memory then push out the clips either side and flick up the memory from the top then pull out. fitting the new is the reverse procedure. Some laptops not sure about the Sony have an empty memory bay so you can add more. If your doesn't then just remove 2gb stick and insert 4gb stick