Plug the LinkStation directly into your PC.
Ensure that you're using Cat5e or better cabling.
Ensure that you're using a 1000BaseT (Gigabit) network adapter in your computer.
Ensure that the computer has sufficient processing power (and isn't busy using it on some other application).
Ensure that the LinkStation is not running DLNA. Turn off web access. Turn off FTP. (for the sake of testing)
Ensure that the LinkStation isn't busy spooling a print job or transferring some other file. In fact, re-initialize it.
Try your file transfers again. Upstream I generally get 7-9MB/sec. Downstream I usually get 14-22MB/sec.
If you still aren't getting adequate transfer speeds, don't assume it's the NAS's fault; it could be your NIC or your PC.
If you do get good transfer speeds after all this, start adding in options and seeing if you continue getting good speeds. For example, now connect through the router (Cat5e or better, again, both PC to router, and NAS to router). Test again. Next, turn back on web access. Test again. Set up port forwarding on your router, test again, and so on, until you're back to the functionality you desire. If at some point suddenly the throughput drops off, take a step back and ask what you just changed that resulted in the drop.