Every registrar has a different process for updating name servers. Most registrars will allow you to log into their website and update your name servers through their customer interface; however, many registrars do not have a method for you to update your name servers other than contacting them.
If your domain from us, you can follow http://cp.eyhost.biz/kb/servlet/KBServlet/faq456.html this insturction to update name server IPs.
Now you have to create A record for the nameserver from your hosting server.
If you want to create NS1.domain.com and NS2.domain.com, now you should login your WHM and follow the bellow instrustion.
WHM -> Edit DNS zone -> domain.com -> created ns1 and ns2 A records and pointed them to new IP addresses (ns1 and ns2) of new server.

Please note: When changing name server IPs at the registrar, there will be 24-48 hours of DNS propagation time during which your website and email may not be available.