The iOS 6 beta 4 is available as an OTA delta update or could be grabbed through iOS Dev Center using a developer account. iOS 6 beta 4 is integrated with bug fixes and improvements.
Warning: Jailbreakers and unlockers must stay away from this latest iOS 6 beta.
It is expected that Apple will release final iOS 6 to public in this fall probably on 21st September, 2012.