are you talking about making brand new name servers?
it is quite a long process.
first login to your registrar.
goto the dns/nameserver admin page
next enter your IPS that were assigned to your server and the ones you want to use for your name servers and the names you want.
i.e.
ns1.mydomain.com
24.66.77.22
ns2.mydomain.com
24.66.55.33
then once that is done,
you have to add your name servers to the dns in direct admin, just login as admin hit the dns admin and add them there.
after that edit your ip files like i said above.
give it 24-48 hours and everything should work.