The easiest way of doing this is to login as root and run the command "sys-unconfig". This command will remove all system ID information and on reboot, the OS will run sysid. Something like the first step of a Solaris Install. You can enter the nodename, IP Address, Subnet mask, Naming Service information, Default Gateway (Solaris 9 or greater), Time Zone, etc.
It is really quite painless.