NameServer (NS) records are what enable your website domain (ex. mywebsite.com) to be found on the internet.
To change your NS records:
Contact the company that registered your domain name (ex. GoDaddy, NameCheap, etc.) and ask them to change your Name Server (NS) records.
Most domain registrars also have a web interface that you can use to change your NS yourself.
It normally takes 24-48 hours for the NS change to take effect.
If you need help:
Your domain registrar likely has detailed instructions on how to do this. Here are instructions from a few of the common registrars:
Changing NS records can seem intimidating but it's a fairly straight forward process and only needs to be done once!