Unlike WordPress, there is no "Forgotten Password" option that will allow you to reset your password if you've lost it. There is one of way of doing changing the password and that is by making some changes within the database itself.
The first thing you would need to do is to login to cPanel
Once you are logged in click on the option called "phpMyAdmin"
You will be automatically redirected to an interface where all your databases can be seen.
If you click on your database you will see all the tables for it. What you are looking for is the _users tables:
In the _users table you can double click in the password field and replace it with:
Press Enter to save the new password.
You will see a "1 row affected" message and your password will have been changed to secret.
Login to the back end of your Joomla site with your admin account and the password secret and change your password to something more secure.
You have now successfully changed your password to something else!