Can you please teach me to upgrade Fedora 30 Workstation KDE of Fedora from Spins to Fedora 31 on the Terminal?
Please, post your repos:
sudo dnf repolist
It looks like you have only official default repos, so you can use the general upgrade method:
I am using Fedora 30 Workstation KDE of Fedora from Spins. Do I have to do clean installation ?
No, follow the link @vgaetera gave you, and that’s all