1. Login into Your Client Area using your registered Email id and password.
2. Click Goto Domains Menu and click on My Domains. Here is the list of domains purchased by you.
3. Click on that domain who's name servers you want to change.
4. Click on Nameservers tab and enter/edit your nameserver as you want. Minimum 2 name servers are required.

5. and then click on Change Nameservers
After That please wait untill it updates to all locations it may be takes 24-48 hr. to update completly.