Since I have to look this up each time — here are the commands to upgrade Fedora to the next (n+1 or n+2 version)

Presupposes the system upgrade plugin is installed. If not, run:

dnf install dnf-plugin-system-upgrade

To upgrade, run:

NEWVERSION=39
dnf upgrade --refresh
dnf system-upgrade download --releasever=$NEWVERSION
dnf system-upgrade reboot