Access to NAS in LAN from WAN

Hello, i've been trying to get this to work by until now i've had no luck :(
I've just bought a NAS from Qnap, the 201TS unit, i have it installed and there is no problem when I try to access it using one of the computers in my LAN.
The problem is when I try using another computer that is not in my LAN to access it using the WEB. And I really need to be able to access it through the internet. eg.: I'm in college and i need a .doc that is in the QNAP what configuration do I need to change in the router in order to access the QNAP using the internet?
I've set it up with static IP (192.168.1.4) and i've created a DYNDNS account, what do I have to do to have access to that IP when I'm outside the LAN?
My router is an Asus WL500gd sorry for any bad english and thank you in advance for any solution you might have for my problem.
Thanks

you might want to add port-pass-through to the virtual server in the web interface

If you want to have a secure access to your data, read something about ssh tunnels