Press and hold any of the apps and after a couple of seconds or so they should start to shake. Then press the 'x' in the left corner to delete the ones that you don't want, and when you've finished deleting press the home button so as to stop the shaking. You cannot delete any of the Apple built-in apps e.g. Music, App Store, Game Centre etc. If you don't get the 'x' on any of the apps that you've downloaded then check that Settings > General > Restrictions > Deleting Apps isn't set 'off'