Check your motherboard specs, it really depends on your mobo if you can upgrade. If you currently have ddr2 ram you will need more of the same. But check if your motherboard supports more ram, that way you dont spend that money
You have to change your motherboard and/or processor to upgrade from ddr2 to ddr3. Unless you upgrade those then you're shit out of luck and have to stick with ddr2. Sorry bro #feelsbadbro