downgrade from windows 10 to windows 7

Hey I was on YouTube last night trying to figure out how to go back to windows 7. I was forced to update. Where is the best place to get a copy of windows? I went on Microsoft webpage and they have changed things so you can’t get a copy I believe. I just downloaded a link from a website...

I have an expensive piece of software that runs on Win 7 that would be even costlier to run on Windows 10. I have a spare Windows 10 machine (a Lenovo tower). I've been looking into installing Win 7 on it (32 bit Win 7 is fine). I'm looking for the cheapest and easiest way to do this. Any...