HariesDesign.com - In Joomla sites, you can change group access level to manage sites. For example : you need a person to manage your site, and change it from registered level to administrator. How can to do that? Its easy,follow this step 

Login as admin ( super administrator ), and the go to Site > User Manager 

select who wants to be your site admin

Change group access level from Registered to Administrator

Press Save or Apply

Done