Here are the normal steps:

1. Login to Domain Register Client Area (My domain provider is Namecheap.com)
2. Click Manage Domain (yourdomain.com)
3. Register Nameserver
4. Create or Modify a nameserver ns1.yourdomain .com > youripaddress
5. Go to domain nameserver and point it to your newly created nameserver (ns1.yourdomain.com) or leave it the same if you just modified the IP address.
6. Update the information in Lxadmin