I recommend
filezilla for an ftp client
your details should be:
server/domain: "upload.ntlworld.com"
username: your account name
password: your password
as detailed here :
http://www.ntlworld.com/help/settings.htm
be aware however that NTL restrict ftp access to their own IP range.. so if you try to access it anywhere else (at work for example) you won't be able to get into it