@action9000: "Upgrading" to Windows 10 is NEVER a good idea. When you upgrade an Operating System, a lot of problems can crop up. Not only right after installation but even months later in some cases. If you want to upgrade, you absolutely MUST do a clean installation if you want to avoid a lot of headaches.
There's another reason upgrading may be problematic when going from an older Windows to the latest version: file loss.
Usually upgrades should keep the files intact. I remember upgrading my sister's laptop from Vista to 7 without any loss of data and it ran just fine. It might have been better with a clean install, but my sister only had an upgrade disc, so a clean installation was not really an option. In the end, though, at least she didn't really see any corruption of her personal files.
However, a friend of mine had another friend who upgraded from... I want to say it was Windows 8, or maybe it was 7, to Windows 10, and he ran into problems right away. There is some sort of issue with the upgrading thing with Windows 10 and some people have suffered loss of data. For him, despite the act that he clicked the option to upgrade, it actually did a clean installation. Or behaved more like one anyway, and his personal data was overwritten.
Naturally, he panicked as he tried to see where they were. Some people say they were moved, but he still couldn't find them. He eventually had a friend of his who was knowledgeable in computers com over and try to recover his data.
Good news: some data was recovered
Bad news: he wasn't able to recover everything
So there's another reason to add to the list of "why you shouldn't upgrade and instead choose a clean install". At least with the clean install, the need to backup data is a lot more apparent. I'm pretty sure it even warns people that they should upgrade. With an upgrade, the gimmick is that you are supposed to keep your personal data, but with this glitch going on, it is possible to lose that data and it's hard to get back.
I am not sure if Microsoft fixed the upgrading issue yet or not.