Upgrading Win 7 to Win 10

[Jimjam]

Slightly off topic, but I know many of you are delightfully helpful nerds.... Please help me!

Anyone know of a way to upgrade from win7 to win10 for free without having to reenter your product key?

I formatted win7 and installed win10 but it failed to activate as it didn't recognise the hardware. Unfortunately the product code sticker was illegible.

I managed to use recovery drive to reset to an activated win7 install.

If I use the upgrade tool to go to win 10, instead of a fresh install, will the computer activate properly?