Microsoft is making Windows 10 available as free upgrade for qualified Windows 7, Windows 8.1, and Windows Phone 8.1 devices. It will be available starting July 29, 2015; people can reserve their free upgrade today. When you upgrade, you’ll stay on like-to-like editions of Windows. For example, Windows 7 Home Premium will upgrade to Windows 10 Home. Find the full list below.
Windows 7 SP1:
| From Edition | To Edition |
|---|---|
| Windows 7 Starter | Windows 10 Home |
| Windows 7 Home Basic | |
| Windows 7 Home Premium | |
| Windows 7 Professional | Windows 10 Pro |
| Windows 7 Ultimate |
Windows 8.1:
| From Edition | To Edition |
|---|---|
| Windows Phone 8.1**** | Windows 10 Mobile |
| Windows 8.1*** | Windows 10 Home |
| Windows 8.1 Pro | Windows 10 Pro |
| Windows 8.1 Pro for Students |
“N” and “KN” editions follow the upgrade path of the parent edition (e.g., Windows 7 Professional N upgrades to Windows 10 Pro). Some editions are excluded: Windows 7 Enterprise, Windows 8/8.1 Enterprise, and Windows RT/RT 8.1. Active Software Assurance customers in volume licensing have the benefit to upgrade to Windows 10 enterprise offerings outside of this offer.
Source: Microsoft