It depends on the system you have there, if you post more details we could give a more specific answer but basically
see how many ram slots you have, and how many are occupied, it could be as simple as adding sticks to the empty slots,
if you have two slots and both are occupied, you will need bigger capacity ram sticks, and that would require us to know how much ram the system can handle, what speed ram it needs etc,
first move is check if you have any available slots though,
Moto