Summary
Windows 10 was released with a free upgrade offer that lasted for 1 year. Now, the free upgrade promotional period is officially over. However, you can still snag yourself a free license of Windows 10, perfectly legally, if you know how.
It is a good idea to secure your important data before proceeding with any upgrade or installation.
Details
Use a Windows 7 or Windows 8.x product key
While the free upgrade offer ended last year, Microsoft will still let you install Windows 10 and activate it using a valid Windows 7 or Windows 8.x product key. When you download Windows 10 this way, your PC will receive a digital license valid for the life of the device, exactly the same way as if you had taken advantage of last year's offer.
First, you'll need to find your product key. See my article "How to recover your Windows product key" for more information.
When you've found your product key, head over to the Download Windows 10 website and click the Download tool now button.
When the tool finishes downloading, open it, accept the license terms, and hit Upgrade this PC now. If you prefer, you can also select Create installation media for another PC to download an .iso file and clean install Windows 10.
If you choose to create installation media, make sure to download the correct version of Windows 10.
Either way, after Windows 10 installs, you can use your Windows 7 or Windows 8.x product key to activate when you are asked.
Assistive Technologies Offer
Microsoft is offering Windows 10 for free for customers who use "assistive technologies". All you have to do is visit their Accessibility website and hit the "upgrade now" button.
A tool will be downloaded that will help you upgrade your Windows 7 or 8.x machine to Windows 10. The process is the same as last year's free upgrade process. When you download Windows 10 this way, your PC will receive a digital license valid for the life of the device, exactly the same way as if you had taken advantage of last year's offer.
According to the terms, anyone who uses "assistive technologies" qualifies for the upgrade. These technologies can range anywhere from magnifiers and content readers to simply using a high contrast Windows theme or mouse pointer.
Despite the terms being clearly laid out, Microsoft is not checking that whomever downloads Windows 10 this way uses assistive technologies. And despite confusion when this loophole was discovered long ago, Microsoft has not hidden or withdrawn the offer. They also have not specified when it will end.
Reinstall Windows 10
If you took advantage of the free upgrade offer, or you obtained Windows 10 using the methods in this article, you can reinstall Windows 10 on that same machine however many times you'd like without providing a product key. This is because Windows 10 registers your hardware IDs with Microsoft's servers, so that when you reinstall Windows, your hardware is automatically matched with the servers and activated.
Windows 10 also allows you to upgrade various hardware components like RAM or storage devices without requiring reactivation. This is also thanks to the ID matching system.
