For security reasons, you will not be able to retrieve your lost password. However, you will be able to reset / change your password by logging into phpMyAdmin.
Log in to your hosting account as an administrator and launch phpmyadmin. If you have multiple databases, make sure your Joomla database is selected before clicking on the SQL option at the top of the screen.
Copy and paste the code in bold below, making sure to change YOURPASSWORDHERE to your newly chosen password and your YOURUSERNAMEHERE to your user name. By default, the username for Joomla is ‘admin’.
UPDATE `jos_users` SET `password` = MD5( ‘YOURPASSWORDHERE’ ) WHERE `jos_users`.`username` = “YOURUSERNAMEHERE” ;
Click ‘go’ to submit the query.
Make a note of these details on a piece of paper and store it in a safe place. Your new username and password should now be working.