First I tried to do a reset, but it was´nt possible.
I then created latest Win 10 install media on USB stick and started the procedure
When restart took place, I got message, that layout of GPT was not optimal, cancel or proceed?
I then manually had to point out the partition to put W 10 on.
This happened every time a restart took place.
So finally latest W 10 was installed, and I had to reinstall my apps.
I think, that this "bad layout" of GPT caused the problem regarding failing to update W 10 to 1709.
So now is the question: how to fix bad layout of gpt?
Again thank you very much for the time and effort, you have spend trying to help me.