Earlier this month we posted that it was possible to update from iOS 6.x to iOS 7 beta 1 without a registered developer device. It appears that this update procedure extends to the latest beta; however, please remember that you must do an UPDATE not a restore.
As of yet, we have not confirmed that this works via the downloadable IPSW. If you've confirmed this please let us know in the comments.
As a reminder, if you would like to downgrade to iOS 6.x, you can do that by following this tutorial.