Just upgraded Windows 7 to Windows 10
It's easy if you have a valid Win 7 or Win 8 (valid includes cracked!)
Details available in Microsoft site.
If you don't want to wait until you get download notification after reserve your upgrade, just download and install Media creation tool then upgrade or make a bootable USB stick/ DVD to install to another computer(remember, it should have a valid Windows 7 0r 8 in it. Otherwise you need to provide product key which is only with purchased copy).
Depending on your machine, it takes 45 minutes to 1 hour to finish Windows 10 upgrade.
Windows 10 is fast with many new features.
If you don't like and wish to get back to your previous OS, it's possible within 1 month.