Uninstalling Virtualmin
There are many levels of "uninstalling" Virtualmin. The most extreme is using the --uninstall flag of the install script:
sh install.sh --uninstall
This is a rather haphazard uninstall routine, that will remove pretty much everything Virtualmin installed (there may be a few stragglers that were installed to resolve dependencies).
Note This should never be done on a system that is in production. It is very destructive. It is primarily for use when you tried an installation option (for example using nginx instead of Apache) and have decided to change after trying it out.
Downgrading Virtualmin Professional to GPL
If you no longer need the features of Virtualmin Professional, but wish to continue to use Virtualmin on your system, you can downgrade quite easily.
In its simplest form, you merely install the Virtualmin GPL module over the Virtualmin Professional module. How that is done depends on your OS and how Virtualmin was initially installed.
RPM-based systems
On RPM-based distributions, like CentOS or RHEL, download the latest Virtualmin GPL RPM from http://software.virtualmin.com/vm/6/gpl/universal/
Then install it using RPM with the --oldpackage option. For example:
rpm -Uvh --oldpackage wbm-virtual-server-4.17.gpl.noarch.rpm
If you were also using our yum repository (which is true if you used install.sh to install Virtualmin), you will need to switch the the GPL repository. To do that, install the latest version of the virtualmin-release package for your operating system and version. For example, for CentOS 7, you could run the following command:
rpm -Uvh --oldpackage http://software.virtualmin.com/gpl/centos/7/x86_64/virtualmin-release-latest.noarch.rpm
apt-based systems
On Debian and Ubuntu systems update /etc/apt/sources.list to point to the GPL version of the Virtualmin repository for your OS (merely insert gpl into the path just after the domain name). That would look like this on Ubuntu 18.04:
deb http://software.virtualmin.com/vm/6/gpl/apt virtualmin-bionic main
deb http://software.virtualmin.com/vm/6/gpl/apt virtualmin-universal main
Once apt has been reconfigured, you can use apt-get to install the GPL version of the webmin-virtual-server module.
.wbm-based installs
If you didn't use packages, and instead used the .wbm format of module, download the latest version of the virtual-server module from http://software.virtualmin.com/gpl/wbm and install it using the Webmin modules module, found in the Webmin menu under Webmin:Webmin Configuration:Webmin Modules.
Final steps
Once you've downgraded the virtual-server module to the GPL version, you can change the /etc/virtualmin-license file to :
SerialNumber=GPL
LicenseKey=GPL