If you have created too many FTP User accounts and some of these have not been used, and you want to remove an FTP Account, then you can accomplish this by following this tutorial.
1- Log into your cPanel account.
2- In the Files section, click on FTP Accounts Icon.
3- Under the FTP Accounts list, click on the Delete button.
4- Click on the Delete button and your FTP Account will be removed.
Warning: Do not use the Delete the Users Home Directory option. Otherwise, the data inside your FTP User account will also be removed and will be unrecoverable until you restore it with a backup.