You may install the iOS 7 Beta 6 by downloading the right files from HERE.
Or if you are already on iOS Beta 5, you can simply OTA and update from the iOS device. However, there is still a configuration file that needs to be downloaded and install.See below.
This update addresses an issue with iTunes in the Cloud, where some purchases may download or play unexpected items. If you have any devices running previous versions of iOS 7 beta, you must:
From your iOS device Safari browser, you may download the ResetMusicAndVideosLibraries Profile from HERE.