Deleting a subdomain
You ca delete a subdomain easily if that subdomain is no longer needed for your current website, please note that deleting a subdomain only remove the pointing configuration from the web server, it does not delete the subdomain folder nor the content that is in it, you will have to manually remove the subfolder if you do not need the content within anymore. This is a precaution approach by Cpanel as user's content is usually untouch when it comes to deletion.
To delete a subdomain:
Click Subdomains button on your domain hosting account control panel.
Select the subdomain to be deleted from the drop down list.
Click Delete button to complete the deletion.