This applied if the host is using DHCP 

Make sure that the hostname you want to use is in /etc/nodename;
the contents of that file will then be used to set the hostname.
(Note that it is essential that the hostname you put into /etc/nodename
is terminated with a carriage return.

 

IF it set manually... look for these files:

Change the hostname in the following files:

/etc/nodename
/etc/hostname.*interface
/etc/inet/hosts
/etc/inet/ipnodes

and rename directory under /var/crash

# cd /var/crash
# mv oldname newname

then reboot the server.