The latest release of Xibo CMS at the time of writing this message is 3.3.2.
Please note that there is an issue with 3.3.2 that can cause a high load on your database in some circumstances. More information about this can be found in the 3.3.2 release blog post. With this in mind it would be best for you to upgrade to 3.3.1 for the time being and wait for the 3.3.3 release.
Please also note that you should not upgrade directly to 3.3.1. You should first make sure you upgrade to each of these versions, to ensure the incremental changes are added to your installation.
You should also make sure that you make a backup of your CMS media library and database before each upgrade is attempted. Once an upgrade is complete, test the CMS to make sure there are no issues before proceeding to the next version upgrade.