Downgrading improperly upgraded site
Permalink
http://www.concrete5.org/documentation/installation/upgrading_concr...
Paying special attention to:
If you're using concrete5.4.2.1 or earlier, you'll need to upgrade to concrete5.4.2.2 first.
Be sure and backup the entire directory structure and the MySQL database so you can roll-back in case things go "wonky"...
Unfortunately, that means you cant simply move c5 back that far unless you have a database backup from before the upgrade that you can restore alongside reverting the C5 dashboard and fixing config/site.php and possibly .htaccess.