Activating your copy of Windows 10 has gotten far less tedious in Microsoft's first major update for the operating system. You no longer have to start by upgrading from a previous install of Windows 7 or Windows 8.1 to get Windows 10 properly activated under Microsoft's free-for-a-year policy. Now, the company will recognize any valid activation key from those prior versions (or Windows 8) and grant you a "digital entitlement" that makes your install of Windows 10 fully legitimate.
Technically, Microsoft says this is meant to work only when Windows has previously been activated on the same device that Windows 10 is being clean installed on. But testing of recent Insider builds has revealed that the company — at least for now — is being pretty generous with the new activation policy. So if you've got an unused key for an older Windows release, you might be able to make the jump right to 10 without any annoying upgrades in your way. There are many more improvements and fixes in the latest Windows 10 update, and you can read about them here.