I am currently running Win 8.1 in my PC. I got 1TB internal HDD and only 50 gb free. Problem is my win 8.1 is installed in a GPT Disk. I wan't to upgrade from Windows 7 to Win 10. For that I'd have to format the my Internal 1TB HDD and then create MBR. I can't do it because I can't backup 900+ gb of data as of now. So I am thinking, I got my 1tb external HDD and I got 40 gb free space in that. If I install windows 7 in external drive and upgrade to 10 then when I am upgraded and activated to Windows 10, I can just remove the external HDD and Format my 150 gb C:/ drive partition of Internal HDD after backing up its data. I can then install Windows 10 fresh on C drive (150gb) Internal HDD 1TB. The problem is I am installing win10 on a different HDD now. I know Microsoft will have my Hardware ID for activation by now. So if my hard disk is changed, will win10 stay activated after a fresh install on a different HDD? That's the only solution I can think of regarding the GPT MBR dilemma. If you got better and an easy method please share. Thanks.