Is it possible to upgrade to/clean install windows 8.1 with an iso on an existing windows 8 installation?

I hava an oem license of windows 8 core & I want to upgrade to 8.1 .
Since my internet connection isn't reliable it's hard to get the update from windows store app. So I'd like to download an iso of windows 8.1 which is unofficially availabale.
After I do the installation(with a generic key,if required) will I be able to activate with my windows 8 product key?