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,
We cannot answer this question without information about your system. At the very least, what memory do you have already? Ideally, tell us which motherboard you have, whether you have any empty DIMM sockets, what operating system are you running, and what you are attempting to achieve?