If you EVER upgraded to Windows 10 during the official free upgrade period, even if you rolled back to an older version later, then you would be able to reinstall Windows 10 at any point in the future and have it activate.  If you never "claimed" your upgrade during that period, then Microsoft specifically says that free upgrades to Windows 10 are no longer available.  They were officially only available for a year after Windows 10 originally launched, and then for an extended period for users who used "assistive technology devices".  Some people have found that Windows 10 will still activate using keys from older Windows versions, but I tested that about a year ago on a batch of Dell systems that had OEM Windows 7 keys.  I tried both an in-place upgrade and a clean install of Windows 10, and in both scenarios, the activation failed with an error that the key I was using was for an older version of Windows, plus a link to the Microsoft Store to purchase a license.  So at best, your chances of a free upgrade at this stage are murky, which means that if you want to attempt this and would not be willing to pay for a Windows 10 license, I would strongly recommend capturing an image backup of your hard drive before upgrading so that you can easily roll back.  Then again, Microsoft will stop providing security updates for Windows 7 in just over a year anyway, so if you plan to keep your system much longer than that, you may as well buy a license if you find the free upgrade isn't available.
Hello, I have heard with Windows 10 1809 which is the current version of Windows 10 if I am not mistaken will accept all Dell OEM Windows 7 and 8.1 product keys and upgrade to Windows 10 through the proper edition. Is this correct? So now this means I have a second chance to upgrade my XPS laptop that I have never upgraded yet?
Windows 10 Upgrade from W7