Besiktepeo :
So i upgraded Windows 8.1 Pro 64 bit to WIndows 10 Pro 64 bit for free and lately my PC got screwed up with an update and i need to reinstall windows so in order to reinstall would I have to go and do the Windows 8.1 setup or Windows 10 setup?
Since you are doing this on the same hardware, you don't need to start over with Win 8.1.
Download the Win 10 ISO, create your install media (USB or DVD), and do a clean install.
Since your current hardware was Upgraded to Win 10 from a valid qualifying OS, and activated...that hardware and previous license is registered at MS.
It should activate new problem.