Upgrade from Windows 7 Ultimate to Windows 10.
Upgrade from Windows 7 Ultimate to Windows 10.
There is a 50/50 chance it will work. Try it, if doesn't work, go buy a new key
Use the upgrade assistant. If it doesn’t help, you can run Windows 10 without a serial key as long as you wish.
Visit the official Microsoft site and install the software. After downloading, select the upgrade option to proceed to Windows 10 Pro. I've successfully completed this process before.