Amateur question--apologies in advance

[govinsh]

I bought my domain from register.com. To switch over, do I have to change the DNS server IP to Jaguar's name servers they gave me for my "NIC records" (66.227.56.27 & 66.227.63.0)?

Sorry. I just don't know what NIC means...

Many thanks to anyone who can sort me out!

[gerilya]

You *can* change the DNS server, but you don't have to.
If you choose to use ns.jaguarpc.net and ns2.jaguarpc.net as your nameservers, it will be easier for you to set up and maintain the site, but if these nameservers go down, your site will be inaccessible.
Alternatively, you can use register.com' Domain manager to have your domain to be resolved to the IP address you have been assigned when you signed up. If you choose this way, do not forget to properly set up MX record too.