That laptop requires DDR3 RAM (Notebook RAM, not desktop as well) And supports 1600Mhz as its top speed, with 4GB of Capacity per slot.
You currently have 2GB of space filled with 1600Mhz RAM, inside a single slot. Your most efficient decision would be to simply purchase another 1600Mhz 4GB stick, and stay at 6GB of 1600Mhz RAM.