It's a bit more complicated than that...you need to find out what type of RAM is in your computer and up to how much your system will recognize. Furthermore, you need to make sure that you have available slots to upgrade.
Use CPU-Z to figure out your memory type by clicking on the Memory tab:
http://www.cpuid.com/download/cpu-z-143.zip
Once you have ascertained that, then you should click on the SPD tab and find out how many slots you have and how much is in each slot by clicking on the drop down menu.