Socket 1366, as I think you have, is quite limited in upgrade options. Sandy Bridge or Ivy bridge are not compatible.
The upgrade would be within the i7 9NN family, with 970 or 980 being the main upgrade options. But since the difference for 970 is 6 cores instead of 4, it depends a lot on what workloads you have, as games so far seldom benefit from more than 4 cores anyway.