The new version of iOS-5.1 beta 2 has been seeded to developers only on the dev center, Only registered developers can download it. This update fixes the bugs and also added thedelete option in ICloud Photo Stream, so that users can delete their photos from Photo Stream.
Photos taken using iOS 5.1 can be deleted from Photo Stream on your device and will be removed automatically from Photo Stream on your other iOS 5.1 devices. Older photos can be manually deleted from your iOS 5.1 devices.
iOS-5 was a big release pushed in October, the new release iOS-5.1 beta 2 is only available for developers yet. All the downloading links are available on Dev Center. In-order to sign up for a developer account, you can visit their official website and you have to pay 99$ per year. This Developer Account benefits you that you can update to latest version before public release and taste the new improvements.