There's a couple of ways to find out what type of RAM you need.
A good freeware application, is SIW
You can also go to a site, like Crucial
, or Corsair
, plug in your system specs (Make and Model of your computer)
, and they will tell you what type of RAM, and how much, you can use.
For installing RAM, Crucial has a decent tutorial
, that shows you how to do it.