So you saying you want to be able to access it from you local network, and over the internet?
A simple way would use FTP I am guessing thecus 5200 supports FTP. But it isn't a very secure way to transfer files.
All you need to do is open a port 20 and 21 on you network firewall/router, and port it to the thecus 5200's ip address. (Make sure it is set static so the IP doesn't change, or set so the DHCP server to reserves a specific ip address.)