Please check your VPS panel,
there you will find everything what you need.
For changing Host name you can use below button.
and change it to your desire Host name
OR
you also can check or change Hostname through terminal directly
Type following to check your vps's current Hostname
and type following to change your current vps's hostname to your desired Hostname(which i named
yourdesiredhostname.com)
hostname yourdesiredhostname.com
I guess you must be knowing how to install Virtualmin.Then also if you having problem in installing it then you can view this tutorial -
https://www.digitalocean.com/community/t...n-on-a-vps