Along with iOS 7.1 beta 3, the latest beta version of iOS has the ability to delete unwanted, but already downloaded update files. The downloaded update can be found in your usage list in Settings>General>Usage. To delete the file, swipe it from right to left, then tap the delete button on the next page.
Previously, the only way to delete downloaded iOS update files was to do a factory restore on your device.
No security changes as of yet, which cannot be said for the full release. Small UI changes to the Photos.app icon for the iPhone 4 and 4S. Slightly changed "Slide to Unlock" and "Slide to Power Off" text/animation. The ability to delete delta downloads is definitely a plus