The easiest way to change the hostname is via the vSphere client (see this post for changing IP address and VLAN IP). If, however, this is not an option for some reason, the hostname can be changed from the service console the following way:
This KB article actually explains most of the proces which includes:
1. Open the /etc/hosts file with a text editor and modify it so that it reflects the correct hostname.
2. To change the default gateway address and the hostname, edit the /etc/sysconfig/network file and change the GATEWAY and HOSTNAME parameters to the proper values.
3. For the changes to take place, reboot the host or restart the network service with the command:
[root@server root]# service network restart
Note: This command breaks any current network connections to the Service Console, but virtual machines continue to have network connection.
I have experienced that after a reboot, the changes are reset and the hostname is changed back to the original one. To avoid this, there is one more step to be performed (before reboot):
Change the /adv/Misc/HostName parameter in /etc/vmware/esx.conf file (see screendump)