Before you even buy the memory for this upgrade, make sure the memory you have selected is the right memory. The best way to do this is by visiting http://www.crucial.com and finding it on this website. See Image.
The tool on crucial.com will help you select the right memory for your laptop. You could buy your memory at Crucial, Newegg, or anywhere you want now that you know what memory you need and how much to get. The manufacturer advises how much memory can go into the laptop - 2GB, 4GB, 8GB - so buying more is not advised as the laptop will simply not support it.