You will find some useful information about FTP in this article.
FTP server is already set up by DH. When you add a domain to a hosting plan, you can choose whether or not enable FTP access on this domain.
If you wish to enable FTP access on your main domain, make sure you have given FTP access to the owner.
Another way of managing FTP server is to create a free subdomain like "ftp.yourdomain.com" with a new user and give FTP access to the subdomain only. It is safer because the FTP access is still diabled on your main domain.
I hope I've given you some ideas. If you encounter any problem with FTP set up, feel free to ask questions here.