Simply use "anonymous" as the user name:
using(Ftp ftp = new Ftp())
{
ftp.Connect("ftp.server.com");
ftp.Login("anonymous", "email@example.com");
ftp.ChangeFolder("uploads");
ftp.Upload("report.txt", @"c:\report.txt");
ftp.Close();
}
Traditionally, this special anonymous user account accepts any string as a password, although it is common to use either the password "guest" or one's electronic mail (e-mail) address.