Windows 7

• Those of you who currently run Windows 7 Starter, Windows 7 Home Basic or Windows 7 Home Premium will be upgraded to Windows 10 Home.
• Those of you running Windows 7 Professional or Windows 7 Ultimate will be upgraded to Windows 10 Pro.

Windows 8.1

• Those of you running Windows 8.1 (the standard edition) will receive Windows 10 Home. And those of you running Windows 8.1 Pro or Windows 8.1 Pro for Students will receive Windows 10 Pro.
• On the mobile phone side, if you're running Windows Phone 8.1, you'll get Windows 10 Mobile as your free upgrade.

So what is the difference between these various editions? You can find out more on the Microsoft blog post about it.