I have two SD cards and each is supposed to hold 2gb. But they actually only hold a little over 1 gig. I need them to hold at least close to 2gb is there anything I can do to format it or something?

I've previously used them for my cannon camera and now I want to use one of them for a digital frame. Actually I am using it but it's only got half the pictures I want on it. I noticed this problem when trying to copy pictures from my PC to the card, it copies some and then errors out. When I then put that card in my camera the camera says memory card full.