Step::2 Go to public_html and then open your WordPress installation directory
Step::3 Find wp-config.php and right click over the file and choose the View option
Step::4 From here you can know the Database Name of your WordPress site
Step::5 Once you know the Database name, go back to cPanel homepage and open phpMyAdmin under DATABASE section
Step::6 Now click over the associated database and then tap on SQL
Step::7 Add the following line in the box
DELETE from wp_comments WHERE comment_approved='0';
Step::8 Click on Go button and then press OK to confirm
This will delete all WordPress comments from your database.
Visit our Blog for more detail. You can also watch the video here