How to install Latest iOS 9.3 public beta ( NO COMPUTER )

This only works with a Apple ID.

Go to apple software beta programme
Click sign up ( it means connects your Apple ID to the beta programme )
Then Tap IOS on that box thing where it says iOS and OS X then scroll down and click Enroll Your iOS device Follow the instructions and install the software profile then go to software updates and it shows the latest iOS 9.3 beta ( this is only a beta ) ( it means a test update ) Do at your own risk

If you want to downgrade back to the normal iOS 9.2.1
Turn of your iOS device Put it into DFU mode
Then it will say Connect to iTunes
Then when it says there was a problem with the device etc that's completely normal just click check for update then click update to iOS 9.2.1 but that will downgrade to iOS 9.2.1 then let it do everything then 5-10 mins later Fresh new iOS 9.2.1 on your device ! Enjoy