Step 1: Login to cpanel
Step 2: Select phpmyadmin under Database
Step 3: Load the tool and execute the following SQL query
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UPDATE `Your_Joomla_Database`.`Your_Joomla_Database_Prefixusers` SET `password` = MD5( ‘New_Password’ ) WHERE `sgj_users`.`username` =’Your_Joomla_Admin_Username’;
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In the above query you should replace Your_Joomla_Database with your actual Joomla database name. Set your database prefix instead of Your_Joomla_Database_Prefix (for example if the prefix is ‘jos_’ the table string will be ‘jos_users’). Enter the new password and your Joomla 2.5 admin username instead of the following strings: New_Password and Your_Joomla_Admin_Username.
Now the admin password will be changed.