Some ISPs block port 21 or maybe you just don't like leaving port 21 open.
If you have a router which does port translation (takes packets received for one port and redirects them to another port) then there's no problem. But if your router won't do that then the following might help
Before you start, it's easy to get the GoFlex Home ftp server to listen on a different port, but the proxy server at Seagateshare.com will not forward requests on other ports.
In that case you would need to know your Public IP address, which may change frequently and this can be a pain. That's the point of the Seagateshare proxy server, to keep track of your Public IP address.
My Public IP address stays for months at a time until I reboot the router, but some ISPs drop the lease routinely and force you to reconnect and get a new IP address.
But if you decide to go ahead then here's how to do it;
First connect with SSH and become root user.
Modify the FTP server
Edit the vsftp config file with the command vi /etc/vsftpd/vsftpd.conf and add a line listen_port =2021
(or any high port number you want)
I should also mention that the vi text editor can be tricky check here for tips on using vi.
Basically type I to enter Insert mode and Esc ZZ to save changes or :q to quit without saving
Restart the vsftpd service with the command /sbin/service vsftpd restart
Open the Goflex Home firewall ports
Modify the firewall config with the command vi /etc/iptables/config and add a line TCP_OPEN_PORTS_EXT="2021"
(or the same port you used when you modified the ftp server)
Restart the firewall service with the command /etc/init.d/iptables restart
Set up your router
Forward port 2021 (or whatever port you chose) to your GoFlex Home port 2021. (I have a Netgear router which only does port forwarding and not port translation)
Make sure UPnP is enabled in the router and GoFlex Home preferences.
Direct your remote FTP client (I use ANDftp on my Android phone) to your home Public IP address at port 2021 (or whatever port you set).