Microsoft officially called time on the free Windows 10 upgrade offer in 2016, but allowed anyone using assistive technologies to continue to upgrade to the new OS without paying a penny.
This offer worked on an honor system -- you weren’t required to provide any proof that you used assistive technologies in order to make use of the deal -- allowing anyone to continue to upgrade to Windows 10 for free. Microsoft finally closed this loophole on December 31, 2017, except (whisper it) the site, and the deal, are still available.
Just click the Upgrade Now button under the statement: 'Yes, I use assistive technologies and I am ready for my upgrade to Windows 10.'
Doing so will download the Windows 10 Upgrade tool and you can run this and follow the instructions to upgrade your device to the latest version of Windows.
Whether Microsoft simply hasn’t got around to ending the deal yet, or -- despite what it’s said -- plans to keep the offer running for a while longer, isn’t clear. But if you do want to upgrade to Windows 10 for free using this method, then you still can. For the moment at least.