Re-booting can often solve it. If your previous version is still there then see if you can find an uninstaller for it in its own folder. Which version did you have before 4.6? If it was earlier than 4.4 than you should go to Add/Remove programs control panel & remove it.

After that if you're still having problems then there is an alternative installer. You just unzip it & use it. See Here about other version. Downld the 'Other' installer.
(I think Murasame's finger is waring out! Beat you this time. Now we're even! lol)