You have to uninstall the old version first by running the “UninstallString” found in the registry: (look around a bit for the DisplayName because its the GUID you’re after.
Then you download the new version and extract it using this command:
Then install the new version here:
c:\download\zune\unzipped\packages\msiexec /i Zune-x64.msi
After you plug in the Zune it looks like it also needs an update: