The ContinuaCI installer supports upgrading in place so there is no need to uninstall Continua CI when updating. The installer will detect an existing installation and ask if you want to use the existing settings or provide new settings. Note that when you update Continua, you should also update all your Continua agents. By default, the installer will also update the local agent, however you will also need to manually upgrade any distributed agents. The agent installer is included in the Continua CI download and the agent installers can be found on the Agents page in the Administration section of Continua.
Continua does not support downgrading. Whilst it is technically possible, database schema changes could result in data loss. Downgrading is not supported and it is highly recommended that you backup your database before downgrading.