You can reset your Joomla administrator's password through the script's MySQL Database.

The most convenient way to manage the database is through the phpMyAdmin tool. Go to your cPanel and click on phpMyAdmin in the Databases box.

Once in the phpMyAdmin select the Joomla's database from the drop-down menu at left. The page will refresh and the database's tables will be displayed on it. Open the SQL tab (look at the top navigation bar).

In the text field write the following SQL query:

UPDATE `jos_users` SET `password` = MD5( 'new_password' ) WHERE `jos_users`.`username` = "admin_username" LIMIT 1 ;

"new_password" - replace this with the new password you wish to use.
"admin_username" - replace this with the username, for which the password needs to be updated.

Once you are ready, click on the GO button to submit the query. If everything goes fine without errors, you should be able to login to Joomla with the new password.