If you are going to upgrade the memory, get the least amount you can since you will probably have to toss (or sell on e-bay) what's in there to upgrade it anyways.

It's real easy, usually remove a screw, pop out the current memory (it usually has two little clips holding it in) and replace it with the new one.

Not all laptop memory is the same, so make sure you get one for your machine and not something that won't fit. If you use the memory configuration tool at any site that sells memory it will tell you what you need by the model.