Thanks Jock1e, I don't own it yet!
It was supplied Ex-factory with "Windows 8", I presume the Medion Restore Disk will re-set to W8.
It's a bit of a beast, (Medion Erazer) with an i7-3630QM CPU and 16GB RAM plus NVIDIA® GeForce® GTX 670MX DirectX® 11 graphics with 1536 MB GDDR5 memory and digital HDMI® audio/video output + NVIDIA® Optimus(TM) technology. It also has a Hard disk capacity: 750.0 Gigabyte and an additional 128.0 Gigabyte SSD.
Not sure in view of its complexity, if upgrading to "W10" would be messy with driver issues etc. Is that offer reversible I wonder?