The following applies to Directnic namservers

Login to Directnic

Go to the Domain Manager
Click on the DNS icon for the website
That takes you to Modify Nameservers
Near the center of the screen is a link that states

   Create nameserver
   You must have a minimum of two nameservers for any domain.

Click on Create nameserver
That takes you to Namesaver creation and the two existing nameserver names and IP addresses
Namesaver Creation
Host Record/Nameserver   IP Address   Delete Nameserver             Modify Nameserver
NS1.SCASP.COM   209.200.237.77         Delete                             Modify
NS2.SCASP.COM   209.200.237.78         Delete                             Modify
To change the IP address you need to click on modify for each name server, and insert the new IP address in the appropriate block, you can only do one at a time.

The formatting on this may not hold, but it gives you an idea how to do it.