First of all, just in case you are asking What are nameservers? Now that is out of the way.
To make DNS changes at HostXNow.com, login to your customer account at https://www.hostxnow.com/clients/clientarea.php and then follow this guide.
1. Click 'Domains'
1. Click on the little triangle (drop-down menu) next to the domain you would like to manage and click 'Manage Domain'.
2. Click 'Nameservers' in the left-hand menu on the page.
3. If you want to use our nameservers you may leave the default nameservers set to be used by having the checkbox selected next to 'Use default nameservers'.
4. If you would like to link your domain to our Shared/Reseller DNS cluster then you may point to your own Private/Custom/Anonymous nameservers by selecting the checkbox next to 'Use custom nameservers (enter below)'. You may also want to do this if you are using your own VPS/Cloud VPS or Dedicated Server. Click the following link if you would like to know how to Create Private/Custom/Anonymous Nameservers. Once you are ready simply enter your Nameserver 1, Nameserver 2, etc and then click the 'Change Nameservers' button to complete the changes.
Note: When creating private nameservers it may take up to 72 hours for these to propagate throughout the internet.