You will also have to uninstall the Regular Labs Library system plugin.
After that you can simply install the older version zip file using the Joomla! Note: Please note that I am unable to provide support on old versions!
With Cache Cleaner you can clean your cache fast and easily via a link in your Joomla! Not only that, it also gives you the possibility to purge expired cache, do a global check-in, empty the temp folder, empty user-defined folders and database tables … Cache Cleaner can clean your cache automatically when you save an article or other item.
And it can clean your cache at preset intervals too.
The upgrade of Joomla itself is a one-click process. Many templates and extensions will not work the same or at all after upgrading to Joomla 3.