Help on Drupal table prefix
If you have access to phpMyAdmin, you can do that manually following this steps:


Login to PhpMyAdmin
Select all drupal tables
With selected: Replace table prefix 
From: {empty}, To: yourprefix_
in settings.php (sites/default/settings.php) change in the database configuration: 'prefix' =&gt; '', to 'prefix' =&gt; 'yourprefix_',
Run cron.