Hi.
The free upgrade to Windows 10 offer from Microsoft expired on the 29th July, 2016.
But Microsoft has a number of exceptions in place for users that missed out on the free upgrade and they have currently not stated any end date to these exceptions, but will adjust as necessary.
You will have to contact MS support and they should be able to assist you with a free upgrade to 10..
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Upgrade to Windows 10: FAQ - Windows Help - Microsoft Support
Cheers.