There are a lot of things to consider here. First, you need to find out what kind of motherboard you have, and see what kind of ram, and how much ram it is capable of supporting. If you can support 6 gigs, then you could theoretically add 4 to what you currently have. However, when you add new ram modules to a system, there is a chance that they won't work with your current module(s). I personally would recommend getting a brand new 2x4gb set of ram assuming your motherboard can support it, and you can afford it.