Step 1: Login to the cPanel.
Step 2: In cPanel go to phpMyAdmin menu in Databases section.
Step 3: Select the required database in the list. You can check the database name of your installation in wp-config.php file.
Step 4: Select the wp_users table, locate the account role you want to change and memorize its ID, you will need it later.
Step 5: Now go to the wp-usermeta table, click on Search. Input the user ID into the 'user_id' field and 'wp_capabilities' into the meta_key field and click on 'Go'.
Step 6: You will see a database cell containing a record specifying the current Role of the user.
Step 7: On the next page, you will need to replace the current meta_value with the new one according to the role you need,
a:1:{s:10:"subscriber";b:1;} - Subscriber
a:1:{s:11:"contributor";b:1;} - Contributor
a:1:{s:6:"author";b:1;} - Author
a:1:{s:6:"editor";b:1;} - Editor
a:1:{s:13:"administrator";b:1;} - Administrator
Step 8: Click 'Go' to complete the setup.