Originally I installed an DDNS update client on my Windows box, but it suffers from flaky RAM and BSOD, so I decided to install the service on my Plex Media Server. It was a simple enough task, but I figured I should write down the step in case it can help anyone else.
Fist, install ddclient on your Ubuntu box:
sudo apt-get install ddclient
Then configure the ddclient:
sudo nano /etc/ddclient.conf
The contents should be similar to the following, using your username, password, domain name obviously:
# Configuration file for ddclient generated by debconf
use=web, web=checkip.dynu.com/, web-skip='IP Address'
You can also determine the update interval by specifying the following in ddclient.conf:
# check every 60 seconds
Hope this is of some use for you. Thanks for reading.