if you dont mind reloading your programs and games. you can use the new windows media creation tool make a new usb bootable stick and boot the pc from a usb stick. when you do unplug the main hard drive so the old os is not tuched. install windows... whe nit ask for a key click skip/i dont have. when windows logs onto the windows validation server on the next full reboot it pull your digital key back into windows and activate windows 10 for you.once windows 10 is activated just update it and then reinstall your programs. with steam all you do is point it to the old steam folder to resysnk it.