Step 1: Login your Cpanel and access PHPMyAdmin
Step 2: Click your Joomla database name in the left menu
Step 3: Click on the table "_users". its depend on your database prefix. if you set prefix as "jos" then database table will be "jos_users".
Step 4: Find the admin account you need to reset the password and click the pencil icon to edit,
Step 5: In the password field enter an MD5 password. You can use MD5 generator available on the internet such as this.
Step 6: After you done copy paste your new password value into password fields, click go.
Congratulations, now your Joomla password has been reset. You can now log in to the new pass.