Upgrade process is described
here. Installer of the extension doesn't support ability to downgrade the extension to old version. If you want to restore previous version, it requires to restore database backup for previous version (we recommend to create a database backup before upgrade of the extension) and then install an old version of the extension.
About your latest post, it is only notice which are generated in Joomla! files. It is not related to "ARI Quiz" extension and it is not affected on extension's functionality.
Regards,
ARI Soft