According to German site Macerkopf.de [Google Translation], the third beta of iOS 7.1 includes a feature that allows users to delete the over-the-air installation files that are automatically installed whenever an iPhone is connected to AC power. Till now, updates downloaded over-the-air could not be removed, an issue that received attention in September after iOS 6 users were forced to install iOS 7 or lose 3.1 GB of storage space to the installation file.

Users with iOS 7.1 beta 3 who have not installed the update will see it listed in the Settings menu, under General –> Usage, where it can be removed like any other app or file. The file can be deleted if it was downloaded over-the-air in the background or manually.

Source [macrumors]