Deleting an FTP account is as simple as creating as creating the account. Deleting the account does not delete the folder or its contents, but it does prevent anyone from accessing that folder through FTP.
To delete an FTP account:
1.) Login to your Cpanel account.
2.) Click on the FTP Accounts link. under the section called "Files".
3.) Click on the Delete link beside the FTP account you want to delete.