Hi, thanks. Samsung Galaxy LTE I9505, presently on 4.4.2.
The full story is a bit complicated. I changed the motherboard and ended up with a Brazilian ZTO CSC. So I want to root with Kingroot (seams very easy), and change the CSC to BTU, and update it to Marshmallow. But I couldn't find how to make a full backup before rooting because meanwhile I put a lot of my stuff in it. It has an external SD card with about 30GB free. When updating with Kies it didn't update without dismounting the SD card, strange.