That's the most open-ended question I've ever read here.
You don't say Dimms or Simms. You don't say dual channel or not. You don't
say if you're retaining onboard RAM, and how many (1 or 2) banks its
occupying.
I would pull out all current RAM, if you can afford it. Replace with the
maximum size RAM module(s) acceptable by your motherboard. Don't buy more
RAM than you need. But, at least 10% unused amount is wise.
always replace all the RAM, as speed mismatch will slow your pc down.
2-4 banks doesn't matter, if you have ram taking up 4 slots then replace 4
if only 2
then replace two, according to your finances.
