Do you have the 2nd Gen Core I processor on your laptop or the 3rd gen? If you want a ram upgrade, you should buy a kit consisting of 2x4GB DDR3 1600MHz rated to run at 1.5v-1.65v, provided you're on the 3rd gen processor. If 2nd gen then you should look at a ram kit of the same prior specs listed here but at 1333Mhz, i.e 2x4GB DDR3-1333MHz 1.5v-1.65v.
Per
this specs sheet, you can drop 16GB's of ram into your laptop. Meaning you can invest in a 2x8GB DDR3-1600MHz kit.