I did this in Windows 8.
Go to Regedit -> Edit -> Find -> Type Itunes64.msi -> Find Next ->
On the left side, There are a lot of folders, find the only open one named "SourceList", go to 1 folder above that, so it should the main folder of the source lest -> Right Click -> Delete -> OK
Now you're ready to install your latest itunest. just close the RegEdit and install itunes64
I just did this 10 minutes ago, hope it helps