I did not upgrade from Windows 8.1 to Windows 10 using the upgrade assistant. I bought the laptop with Windows 10 installed on it.
The reason why I want to ''downgrade'' to Windows 8.1 is that for some reason it seems like Windows 8.1 is a lot more responsive than Windows 10. In my opinion, it is more stable and I don't get loaded with bloatware as @Twilight said.
Yes, I know that you can uninstall it, but let's be fair, Microsoft should just not load the OS with all these nonsense apps.