For the latest version visit www.webmin.com and amend the shortcut in step 2 to the relevant version.
Get logged into your server via SSH and use the following 3 commands:
Step 1:
cd /usr/src
Step 2:
wget http://prdownloads.sourceforge.net/webadmin/webmin_1.500_all.deb
Step 3:
rpm -i webmin-1.500-1.noarch.deb
This will install Webmin to https://youripaddressordomain:10000
You may need to do the following steps if not successful:
Run the following as some modules may not be installed:
sudo apt-get install perl libnet-ssleay-perl openssl libauthen-pam-perl libpam-runtime libio-pty-perl libmd5-perl
If you get errors about it not finding these packages, then enable the universe repositories:
sudo vi /etc/apt/sources.list
remove the # from the universe and multiverse lines and save.
Then update the repository settings:
sudo apt-get update
Run the following to unpack & install:
sudo dpkg -i webmin_1.500_all.deb