Before we go through the upgrade process in more detail, there are a few things you should know. First and foremost, make sure you have a recent backup of your most important files on an external drive, do it now! Second of all, if you’re upgrading from Ubuntu 16.04 LTS, you’ll have to deal with some major desktop changes if you use Unity. Ubuntu 16.04 LTS (Xenial Xerus) uses the Unity desktop environment by default, but Ubuntu 18.04 LTS uses the GNOME desktop environment with a highly customized interface to make it look like Unity, which Canonical said it won’t be removed during the upgrade process and will remain available as an alternative if you still want to use it.