Mate S get to 6.0 Marshmellow

Hello all,

I just got a new Mate S and it's running 5.1.1 - CRR-L09C432B114 and there are no OTA updates available for me.
Custom Version is CUSTC432D001.

Can anyone point me to exact update paths and methods to get to latest 6.0 Marshmellow?

Thanks in advance!