I have my 3DS XL which came with the stock 4GB card. And today I bought an 8GB card. How do I do the transfer? Am I going to need my other 3DS (which I currently don't have) to transfer my games like NSMB2 and all the downloaded stuff I have.

Just copy the everything off the old card onto the new one.

That's how I did it with mine.So I just plug the old one into the computer, cut/paste onto the new one, and everything will work just fine?