Prerequisite
>$ cat /etc/fedora-release
Fedora release 30 (Thirty)
Update software and back up your system.
>$ sudo dnf upgrade --refresh
Install the DNF plugin.
>$ sudo dnf install dnf-plugin-system-upgrade
Start the update with DNF.
>$ sudo dnf system-upgrade download --releasever=31
Reboot and upgrade.
>$ sudo dnf system-upgrade reboot