Restoring Windows 8 After Restoring Windows 7

Question

Windows

Last year I bought a laptop with Win 7 on board.
In November, a promotion was made for the transition to Win 8 (that is, a key was bought, which is still available).
Today, a child accidentally got into the Windows Recovery Enviroment (Ubuntu is installed on the laptop and this is quite easy to do through GRUB).
A couple of times by poking in the wrong place, the child restored Windows to the state at the time of purchase. That is, with Win 7.
Question: how to return an honestly purchased eight to a laptop?

Answer 1

Call microsoft support. There will be a more precise answer.

Answer 2

Try a clean install .

Answer 3

Take a Windows 8 image (I hope you saved it) and install from it, on top of Windows 7. When installing, select "system update". And, accordingly, use the key you have.
I did the same when I changed the drive in my laptop. I put the seven with the key from the sticker on the laptop, and then immediately the eight with the key for updating.