If you're coming from an outside address, you need to configure the router/NAT for port forwarding. If you don't have power to configure that router, you're out of luck, you won't be able to do it.
FTP is a complicated protocol, with two TCP streams. Old ftp actually had a connection from the FTP server going to the client, which complicates things through firewalls and NAT. Passive FTP helps this a bit - if you're going to have any luck at all, I'd make sure I could do Passive FTP on the FTP server.
FTP also sends name/password in the clear.
It would be simpler (and more secure) if you were to use SFTP, which is basically the FTP command set run under the SSH protocol. It is a single port to forward, and the data - including your name and password - is encrypted.
If you do still go the FTP route, you'll need to configure two ports on your NAT for port forwarding (20/21) and make sure your ftp server supports passive FTP.