Use Speccy to find the type of ram it is and the running frequency. Like DDR3 1066Mhz. Check if its normal or low voltage laptop ram. DDR3 laptop ram or DDR3L (again from Speccy).
So find the type - DDR2, DDR3 Laptop ram.
Find the type of voltage - DDR3 , DDR3L
Find the speed - 1066 MHZ
Order a similar spec ram in higher capacity from Amazon (Amazon fulfilled). If it doesnt work return it. A ram may support 1600mhz but might also work in 1066 etc if specified in the details.
Just giving an example of speed .AFAIK, for 1066Mhz, you don't get DDR3L sticks.