mrqs: if its null, then your phones isnt region customised
That means you can use odin and flash up and down at your hearts content and not worry about stuff like waranty. You'll never need to make sure to reflash to the correct CSC before sending it back.
mogden: You're region is german, and II5 is the latest version right now. If you want to downgrade you need to use odin. Search on the forum, there are firmware files available for H2, H4, H7, H8 and II5.