Every registrar has a different process on updating name servers, some don't even have a way without contacting them to do it for you.

For the most part you will be able to figure it out by following the same steps you used to create them originally.

Please visit http://www.brontobytes.com/tutorials/ for detailed video tutorials on hoe to change your name servers.

If you still aren't sure you, will need to contact your registrar.