Beware of tricksters sending out emails that “welcome” you to using Windows 10. Many, if not all of them, are crafted by virus distributors who want you to download a dosed copy of windows or something else. If you’re having difficulty deciding if an email is official, try reading this article – How do I verify that an email message is REALLY from Microsoft?
The bad guys have been using the Windows 10 lure for a while. Here’s some more examples of the trick.
You may find dozens of articles about this problem with a simple search in your favorite browser. You may also find a variety of methods that will let you verify the sender of an email, so you can tell when a non-Microsoft entity is trying to trick you.
If you are thinking of downloading and installing Windows 10 and you current operating system is prompting you, follow your operating system directions and links. Do not use any suspect link in an email, and verify an email link is official prior to clicking it.