I am not an expert & only recently got into "extending" RAM. I assume it means add more RAM and that's what I've recently done on a laptop (very easy) and then on a desktop (slightly more fiddly but not difficult).
If you go to click here you will find a system for finding out exactly what RAM is available for your machine; then order it - crucial are as cheap as anyone else and very quick to deliver. Then yes, you do have to open part of your machine - one of those little "doors" on the underside, opens with a screwdriver and fitting extra RAM is dead easy - and there was an illustrated article about it in pcadvisor mag towards the end of last year. I dithered for ages before taking the plunge and I was amazed how simple it was.