Ok. Done it just now.
Removing the back lid is "hard-hard easy". You need some tools to dislocate the snap at each side.
Installation of the SSD M.2 is easy (I'm using Samsung SSD 850 EVO m.2). Just put it there and screw it. Of course you need to find fitted screw.
I install Windows 10 from scratch. Moving all files from original HDD and format the previous partition of the HDD.
Install the HDD back again and it run smoothly.
On the BIOS I use Legacy not AHCI.
Hope helps for anyone who wants to upgrade.
Cheers