If you'd like to update your nameserver IP address,  you can input the nameserver's new IP address through your account so that the info is submitted directly to the registry.

• Login to your account.
• From the menu on the left select DOMAIN NAMES,and then Register DNS.
• Use the update a nameserver tool in the first section of the page "Register a NameServer Name" to updated your nameserver IP.

The domain must be in your account in order to modify the nameserver details.