You can delete it from your device by holding your finger down on it and pressing the "x" when it wiggles. You can also delete the app in your library on the computer simply by right-clicking it and selecting delete.
The sad thing with iCloud? While you can download any app you've ever downloaded with that account (as long as it is still in the App Store), you can't delete those apps you don't want from the list. I have a ton of apps I only downloaded to test out or to earn game points in other apps and I have to scroll through all of those.