For this procedure you need to enable SSH access to your ESXi host.

You can change the hostname, also fqdn if you want, via two commands. Both will be shown below.

NOTE: In this example, I will change fqdn (meaning hostname.domain).

Via esxcfg-advcfg:

[root@local:~] esxcfg-advcfg -s mini.local /Misc/hostname
Value of HostName is mini.local

or via esxcli command:

[root@local:~] esxcli system hostname set --fqdn=mini.local
[root@mini:~]

In order to see your results, you can use also two commands, as shown below:

[root@mini:~] esxcli system hostname get
   Domain Name: local
   Fully Qualified Domain Name: mini.local
   Host Name: mini

[root@mini:~] esxcfg-advcfg -g /Misc/hostname
Value of HostName is mini.local

Done! ;)