You only have to add the hostname. The IP is handled automatically.
Then, you can remove the old name server by clicking the remove check box to the right and clicking "Save Configuration". Please note this action does not delete the name server entry, it removes it from this domain only.
This procedure assumes that the nameservers in question are valid registered Internet nameservers. All DNS must be listed on the root to be considered valid. Nameservers based on ccTLDs (country-code Top Level Domains, like .ca for Canada) must be manually added by the OpenSRS Support Team - Email firstname.lastname@example.org with the request. Keep in mind the Verisign Registry does not record IP addresses for ccTLD nameservers, so don't be surprised if the nameserver IP doesn't show up on the whois server output.
This means that the IP address you entered is already taken. You may either find another IP or delete the existing nameserver host record.
To avoid additional Registry associated fees required to reclaim and renew a domain after it has expired, it is strongly recommended to renew your domain on time, otherwise you may be subjected to an additional fee known as a "Redemption Fee" (that we pay to the associated Registry) before you can salvage an expired domain and have it renewed.
The redemption fees vary depending on the type of domain you are redeeming:
.COM, .NET, .ORG domains: $100
.CA domains: $75
Note that redemption fees do not include the renewal fee. If you need to redeem and renew an expired domain, contact us. Redemption fees were introduced by the Registry to provide an extended period of time after expiry date to allow an opportunity for registrants to reclaim and renew the domain before it is deleted/released, as well as to encourage Registrants to renew their domains on time.