The great thing about WordPress is that there is "Forgotten Password" option that will allow you to reset your password if you've lost it.
It will ask for the email address that was used when creating that account and send the new password there.
The other way of doing this is by changing the password 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 WordPress site with your admin account and use the password secret. Change your password to something more secure once you are logged in.
On the left hand side click on Users and then Your profile.
At the bottom of the page you will see the following:
Click on Generate Password and remove the characters that are automatically inserted. You will then be able to change it to something else you prefer.
You have now successfully changed your password!