If just your icons are small, you can easily fix it by reading this article:
Resize icons quickly using your mouse wheel in Windows Vista | Vista Rewired
However, it seems to me that you may be using a very high resolution. To fix this, go to your desktop area (the place with all your icons and the background.) Find an empty space, right click and choose personalize. Then click on Display settings at the very bottom. Once you're there, just drag the resolution slider to the left and your screen should appear bigger.