Could be the Acer Aspire M3100, in which case, if only 2 dimm slots filled, yes you can add another 2 dimms of exactly the same size and speed as your original dimms.
Could be the Acer Aspire M3100, in which case, if only 2 dimm slots filled, yes you can add another 2 dimms of exactly the same size and speed as your original dimms.