As WhoSayln and Skilldrick said, you should use ftp to upload files and delete files from the server (if you have permission).
But in your question you say: "I can not delete the downloaded files from FTP." Do you want to delete local files from your computer (those that you just downloaded from the ftp server) or files on a remote server?
If local, then just rm -f filedo it: p
, script ( ), - :
jyzuz@dev:/jean> ftp -n -i remoteserver.com << EOF
> user $username $password
> cd /remote/directory/
> rm filename.txt
> bye
> EOF
? = P