What kind of ram for Macbook?

You do not void the warranty by adding RAM to any computer, Apple or otherwise. Why do people make up this stuff? You do not need any special skill or tools to add RAM to any Apple computer, and you will not break anything unless you do something amazingly weird. Why do people make up this stuff? You do not need to look up online what type of RAM is needed if the computer is working normally. Go to the Apple logo > About This Mac" > More Info > Memory. That shows the type of RAM that is in it now, and that is the type you need to buy. You can mix sizes, but you will get slightly better performance from matched sticks (same size, same brand and type).

You definitely can change a RAM card or both. The key here is first knowing your exact model. If you go to here http://support.apple.com/specs/#macbook you can get it by Serial number of the list. You need to know the exact compatible memory and how to intall it. It should be on the web site. It is not likely that you would have to replace a pair. Used 1G cards on EBAY are $15. There should be other stores also Without a model, I don't want to guess. Replacing Ram has to be an exact thing with an Apple.

I don't even think you can open a macbook without destroying EVERYTHING in it, but I would guess a DDR3-1333 or something around that.

All MacBooks can be open but you will likely break warranty and it generally somewhat complicated. If you are not experienced with taking apart laptops, I wouldn't try it on your own.