Did you know you can now install Apple beta software without having a developer account? Install the corresponding configuration profiles directly from your device to receive over the air (OTA) updates. After installing the profile and restarting your device, you should see the option to update from your settings under your usual system update menu. You no longer have to deal with IPSW imaging.
Disclaimer, these software are still in BETA, so use at your own risk and know that they are more buggy than release builds.