Like raw5y said, FTP is the quickest and easiest to do.
Enter your NAS thru the web browser
192.168.1.1 => EXAMPLE
Log in
Go to Management
Network Management
Dynamic DNS
Now STOP and go to Google and create an account with a DDNS provider, there are several options for free and one offered by D-Link themselves (paid I think) but remember to go for a free one. Once you have an account go back to the NAS
Should look something like this. Once its in success, updated then go to
Account Management
Create
Create one account with the permissions you want, you want READ-ONLY right? then select, select FTP and READ-ONLY, and done.
Now the hard part, go to Network Management
Port Forwarding and expand
Click TEST and hope for the best, if all ok then you're good to go, if not then read your particular router manual and find how to forward the ports (80 is always open but you don't want that one, 8080 or the one the NAS uses, I don't know which one is, read the manual).
If you still have problems call your ISP and tell them you need help to open the ports of your router.
Finally you should have something like this:
ftp://ftp.ebi.ac.uk/pub/databases/blueprint/