First, open the terminal and run the following command to update your system by getting the latest software packages for current version of Fedora you have installed

$ sudo dnf upgrade --refresh

Second, install the special DNF plugin for system upgrade (if you haven’t already).

$ sudo dnf -y install dnf-plugin-system-upgrade

Now, begin downloading update for Fedora XX and upgrade progress by using the command (where XX is the version you want to upgrade to):

$ sudo dnf -y system-upgrade download --releasever=XX

Once you finish downloading the new version, run the following command to restart your system and get into upgrade action:

$ sudo dnf system-upgrade reboot

Upgrading the system will take time (for me it took around 20 minutes), so you can now relax, take a walk, and let it finish.

The above has been tested to upgrade to Fedora 35 through 40

H/T: https://www.linuxjournal.com/content/how-upgrade-fedora-32-fedora-33-cli-graphical-methods