If you are using Linux, it is possible to use wget to update the IP. Here is a sample URL:
https://dyndns.topdns.com/update?hostname=www.example.com&username=myusername&password=mypassword
The above one will detect your IP automatically and perform the update. If you want to update with a custom IP address you can use:
https://dyndns.topdns.com/update?hostname=www.example.com&username=myusername&password=mypassword&myip=192.168.0.1