You need to use a dynamic DNS client. They have a url dynamic.registerfly.com that your dynamic client would post to when the ip changes
No, RegisterFly does not provide a client however we have included links to a number of good software clients you can use.
Java Dynamic DNS Client
IPCheck for OS/2
Please note we are not associated with any of these products. We do not provide service on any of these applications. Please use at your own risk. Some of these listed applications are still under testing.