Find the official instructions on how to update here. You first need to ensure your current system is fully up to date. Then you can proceed to the upgrade to a newer version of the distribution.
Upgrading using the command line is also an option, according to the same procedure as that of a Ubuntu server.
An upgrade from one LTS version to the next LTS, or from one Ubuntu version to the next is officially supported, so is in principle safe. As it is a matter of clicking through dialogs, the process also is easy and new user friendly.
Still, there is a chance that an upgrade does not go well. Before performing an upgrade, and actually before any system maintenance, make sure the backup of your user data is up-to-date.