first of all, you need two things:
- an activated current OS (w7sp1 or 8.1). the eligible channel types that are reported to work with this trick are Retail, OEM:DM (w8.1), and OEM System Builder.
- a copy of w10 ISO via w10 media creation tool that matches the upgrade path (e.g. for w7 Ultimate sp1, you get w10 pro)
the steps are simple:
- validation of the current OS online (this is true for w7, but i haven’t found the online validation process for w8.1). this makes sure MS activation server recognize your current OS as a legit copy.
- generation of GenuineTicket.xml based on your installation.
- retrieve gatherosstate.exe from w10 ISO. this file is located in the sources folder.
- at administrative prompt, run it on your activated and validated current OS. it will generate an xml file, called GenuineTicket.xml. save this file else where, e.g. in a usb stick.
- do a clean install with w10 ISO. skip places that ask you for key.
- once it’s installed, make sure the new OS is not connected to the Internet.
- copy GenuineTicket.xml to C:\ProgramData\Microsoft\Windows\clipsvc\genuineticket\ on w10:
- at administrative prompt, type ‘net stop clipsvc’ and press enter key;
- copy GenuineTicket.xml to the specified folder above;
- at administrative prompt, type ‘net start clipsvc’ and press enter key.
- reboot w10 and connect it to the Internet. the w10 installation should be activated.
the above process is only needed for the first time (as a replacement for normal upgrade paths for the w10 free offer, which caused quite a lot of issues since the official roll-out.). for the subsequent w10 installs on the same device, all you need to do is to do a clean install, and make sure the new OS is connected to the Internet.