After some digging, I found the command to update the external IP stored on wd2go server. The command is in the folllowing http request format
https://198.107.148.110/api/1.0/rest/device_port_forward/119xxx923?
format=xml&rest_method=put&ip=YOUR_EXT_IP&local_ip=192.168.2.5&forward_port=80&forward_ssl_port=443&
device_auth=76e79ee544axxxxxxxxxxxf0e7f250
This command can be executed via web browser. Once executed, the device's ip address stored in wd2go server will be updated accordingly and this will make remote access work again upon IP change by the ISP.
Now, I tried to find a way to run this command in unix environment so that I can put it into a shell script that will update the IP by itself. Here's the command I tried
wget --no-check-certificate https://.........
However, I got this error
HTTP request sent, awaiting response... 405 Method Not Allowed
2014-06-25 13:54:23 ERROR 405: Method Not Allowed.
Anyone know how to execute such command in unix?