Today you can again update your operating system and passing from Windows 7 Pro or Windows 8.1 Pro to Windows 10 Pro, free of charge.
You need only download Media Creator Tool directly from Microsoft website , run the tool and select "update Windows 10" instead of "Using the tool to create installation media (USB flash drive, DVD, or ISO file) to install Windows 10 on a different PC"
Instructions from Microsoft website:
1. Select Download tool, and select Run. You need to be an administrator to run this tool.
2. On the License terms page, if you accept the license terms, select Accept.
3. On the What do you want to do? page, select Upgrade this PC now, and then select Next.
4 .After downloading and installing, the tool will walk you through how to set up Windows 10 on your PC. All Windows 10 editions are available when you select Windows 10, except for Enterprise edition. For more information on Enterprise edition, go to the Volume Licensing Service Center.
regoular Microsoft Windows 7 Professional - Windows 8 Professional activated.
At the end of the process, you can find Windows 10 Professional license activated