First of all, just in case you are asking What are nameservers? Now that is out of the way.
To make DNS changes at Itsyourdomain.com, log in to your account and follow this guide.
1. Click ‘Change DNS/Hosting Info’ and locate the domain you wish to change.
2. Check the tick box alongside the domain and click ‘Continue’
3. Enter the new name servers in the ‘Primary and Secondary Host’ fields.
4. When you have completed your changes, click ‘Continue’ to submit the changes.
Note: You need to enter a minimum of 2 nameservers.
Warning: Do not enter your IP address; this will cause problems.
Remember, it can take up to 72 hours for the changes to take effect.