Personally i use CPUID. This should give you the information you need.
Also check this thread out: How can I add more RAM?
To view the amount of RAM your computer has, go to your Control Panel, click on "System and Security," followed by "System" to view basic information about your computer, including your current operating system, processor, and amount of RAM. To add more RAM, you must open up your laptop to insert additional RAM memory sticks. Make sure to use DDR3L SDRAM memory sticks when upgrading your laptop.
This contains the hardware maintenance manual for your machine.