Installing Webmin on Ubuntu is extremely easy.
Grab the latest version from sourceforge.net, at time of writing the latest is 1.791
$ cd ~
$ wget https://sourceforge.net/projects/webadmin/files/webmin/1.791/webmin_1.791_all.deb
$ sudo dpkg -i webmin*
$ sudo apt-get -f install
Walla! Webmin is now installed and can be accessed at https://server-ip-address:10000