How do I block access to the website or its part at FTP access?

This is implemented by creating and using .ftpaccess file. E.g., to restrict access to FTP by a specific IP address only .ftpaccess shall contain the following data:

    <Limit ALL>
     Allow from xx.xx.xx.xx
     Deny from all
     </Limit>

where xx.xx.xx.xx is the permitted IP address.