If you forget your Joomla admin password, you can reset again from PhpMyAdmin.

1. Login to your cPanel, and go to phpMyAdmin
2. Select your database and click xxx_users
3. Click the Edit link of the user you wanted to reset password
4. Replace Password to "21232f297a57a5a743894a0e4a801fc3" and click Go
5. Now Login to your site backend with 'admin' as username and password
6. Don't forget to change the password from backend.