Microsoft today started sending out notification to Windows 7 and Windows 8 users to reserve their free Windows 10 upgrade. Microsoft has now installed Windows 10 upgrade assistant through Windows update KB3035583.
This update enables additional capabilities for Windows Update notifications when new updates are available to the user. It applies to a computer that is running Windows 8.1 or Windows 7 Service Pack 1 (SP1).
When an user clicks the notification icon, they will be presented with the above screen explaining the process. They need to enter the email address for now and Microsoft will notify them to download when its available. It also explains the new features that will be part of Windows 10.