Due to the large and varying number of different devices out there (routers, cameras, DVRs), It is unlikely that we can specifically troubleshoot your device. That said the general setup for your device is...
Service: (DynDNS.org/Dyn DNS/Dyn)
Domain: exampledomain.com (this isn’t always an option, but this would be the domain of your hostname)
Host: examplehost.exampledomain.com (if the host you are updating is a subdomain, like they are in Dynamic DNS Pro, this will be the full hostname).
Server Address: members.dyndns.org
Username: Your username
Password: Your password or updater client key. You can see if you have generated an updater client key by going to My Account > Account Settings at http://account.dyn.com
Once those fields are completed, your device should start updating the IP automatically once it changes. It would also be recommended to contact the device manufacturer as well for specific troubleshooting with it if it is not DNS related.