Version 4.2 is the first version based on the latest Windows Installer technology.The install kit performs additional steps that detect and uninstall pre-4.2 versions of the product. Once a pre-4.2 version is detected, the uninstall is accomplished by running the uninstall program supplied by the pre-4.2 version.
The difference is that privilege elevation cannot be used when running the uninstall program for the pre-4.2 version. Administrator privileges will therefore be required when upgrading from pre-4.2 releases. This is the same situation that existed prior to version 4.2, when Administrator privileges were required for all install/uninstall operations.