You can change the name servers of your registered domain from client area. For doing that, you will need to log in to your client area first. If you do not know how to log in then follow these instructions
1. Once you logged in, click on Domains -> My Domains .
2. Click on the Down Arrow icon the the right of the Manage Domain button against your domain name for which you want to change the name servers. Then click Manage Nameservers.
3. At the Nameservers page for the domain which for the changes, type in the nameservers at the boxes showed in the following screen.
4. When the nameservers are given in the boxes, click Change Nameservers. All done.