First of all, Voxengo software does not feature third-party ads nor malware nor unexpected bundling. The software is routinely checked for the absence of malware at VirusTotal.
In order to install this product you will need to download its corresponding setup file to the computer you are planning to use this product on (Internet connection is not required for the product to function).
After download is complete you should run the executable and follow instructions presented by the setup application.
You should open the DMG disk image and drag & drop the application package into the Applications folder located on the hard-disk.
Version updates are handled in a similar way. You do not need to uninstall any previously installed version - just install the newer version over the existing one. You will not need to re-enter your authorization/registration details this way.