Using the command line
If you’ve upgraded from past Fedora releases, you are likely familiar with the dnf upgrade plugin. This method is the recommended and supported way to upgrade from Fedora 25 to Fedora 26. Using this plugin will make your upgrade to Fedora 26 simple and easy.
1. Update software and back up your system
Before you do anything, you will want to make sure you have the latest software for Fedora 25 before beginning the upgrade process. To update your software, use GNOME Software or enter the following command in a terminal.
sudo dnf upgrade –refresh
Additionally, make sure you back up your system before proceeding. For help with taking a backup, see the backup series on the Fedora Magazine.
2. Install the DNF plugin
Next, open a terminal and type the following command to install the plugin:
sudo dnf install dnf-plugin-system-upgrade
3. Start the update with DNF
Now that your system is up-to-date, backed up, and you have the DNF plugin installed, you can begin the upgrade by using the following command in a terminal:
sudo dnf system-upgrade download –releasever=26
sudo dnf system-upgrade reboot
Reference Fedora Mag