Regarding Windows 10 re-format/reinstall

Hi guys, how's everyone doing? I am new to the community, i am posting my need of help regarding
to a Windows 10 Professional 64 install, i previously own windows 7 professional 64-bit, my question is simply this
do i need to purchase a copy of windows 10, because i plan on back up everything i already have on my current pc i am currently posting on to this thread, about the possibility of reformatting my drive (once backed up) what really stumps me to a point where i am much pretty lost. Let me try to explain the best i can.

Windows 10 is currently installed.
I don't want to go back to Windows 7
I am asking do i need to purchase a retail copy of Windows 10, or do i use the Windows 7 (disc and wait till its finished installing then try and re-download which i don't see how that would work, i was eligible for a free Windows 10 upgrade, I've owned Windows 10 since day one, i really just want to backup everything and just create a fresh new re-format, but i fear that i may lose my windows 10 regarding, going back to 7. I apologize i made this question sound rather difficult, I've also read the forums rules, and that i kind of searched to see if there was a topic out there similar as mine/relevant, I've browsed the other forums to, because i want to make sure this topic was suitable before i went a head and post to the forum we are in now, didn't want to make any mistakes now!


Thanks in advance guys
hope you all enjoy your Tuesday

Once you upgrade the hardware once, you can then clean install and it will activate...as long as you didn't make a substantial hardware change. If you did change the hardware, you will end up calling MS and they well get it activated for you. Then, this new hardware will be permanently activated, so you can reinstall clean.

As alphanumeric said, skip entering the key during the reinstall. You don't need it.