You can upgrade to the latest version by simply running:
snap refresh xibo-player
You may find that snapcraft has automatically upgraded your Xibo-player snap in which case you may just need to restart your Player.
You can check to see what version of the Player you have installed by running:
snap list
You should see an entry in the output like this:
Name Version Rev Tracking Publisher Notes
xibo-player 1.8-beta1 16 beta xibosignage -
The latest version of Xibo for Linux can also be installed from here: Install Xibo Digital Signage Player on Linux | Snap Store
Please note: There is no requirement to uninstall the old version prior to upgrading