We will soon be publishing Windows 10 as an “Optional Update” in Windows Update for all Windows 7 and Windows 8.1 customers. Windows Update is the trusted, logical location for our most important updates, and adding Windows 10 here is another way we will make it easy for you to find your upgrade.
Early next year, we expect to be re-categorizing Windows 10 as a “Recommended Update”. Depending upon your Windows Update settings, this may cause the upgrade process to automatically initiate on your device. Before the upgrade changes the OS of your device, you will be clearly prompted to choose whether or not to continue. And of course, if you choose to upgrade (our recommendation!), then you will have 31 days to roll back to your previous Windows version if you don't love it.