First time installation
On the downloads page download the calculator.
The downloaded file is a ZIP file with the software. Unzip and run IceCreamCalculatorSetup.exe.
When starting the installation you might get a warning from Microsoft Defender SmartScreen that an unknown application is started. To start it anyway press “more information” and the Run anyway button to start the installation. If you have a Virus program you might also get a warning.
The reason this happens is that this is a free software and it does not have a trusted certificate. A certificate cost quite a lot of money each year.
After the first time installation you will get an update message inside the calculator when a new version is released. You can also download and install manually from the Settings dialog.
Check this page for how to install the calculator on MAC OS.