Help upgrading RAM in R15

Hello

I have 16GB of RAM currently on my laptop, and want to expand to 32GB.

I have the following situation on my Alienware Laptop.

Intel Core i7-4720HQ CPU 2.60GHz

I noted the DDRL 3 that is currently in the system with 2 sticks of 8GB, but I bought similar RAM 2 sticks with 16GB.  It is doing the beep beep deal.

Anyone know what RAM to buy, specifically with numbers, codes, etc?

Thanks

Pete