You can change the nameservers of your registered domain from client area itself. For that, you will need to log in to your client area. If you do not know how to log in then follow these instructions.
Once you logged into the Client Area, click on Domains -> My Domains
Click on the down arrow beside the wrench and select Manage Nameservers
Change the Nameservers of a Domain
Click on Change Nameservers to apply the changes.
