Hypothetical question re Win 10 home upgrade to pro.

[anon(9424572)]

Long story so bear with me.
I previously has a Vista premium/pro laptop which was retired & I bought a Win 7, this came with the Win 8 upgrade on CD with a key - key says it's win 8 pro, before I could install win 8 on win 7 laptop, it failed so received a refund, I installed Win 8 over Vista & eventually installed Win 10.
Now I have a Win 10 home laptop as old one died, can I use the win 8 pro key to upgrade win 10 to pro or was it absorbed into Windows 10 upgrade.
I just want to make sure before I throw the CD & key away that it cannot be used again to install Win 8 or upgrade Windows.

 

[TechFreak1]

I am not sure if this will work, you could try:
settings -> activation -> click on go to store -> at the link below click i have a windows 10 pro product key -> enter your Win 8 pro product key.