The LibreOffice website recommends to update an existing LibreOffice installation on Windows by just over-installing the new version. This usually works, but I experienced that the update does not thoroughly clean up some relicts of the old version. For example, if you updated from 3.5 to 3.6, the following 3.5 relicts will persist:

1.) The old installation directory (such as %ProgramFiles%\LibreOffice 3.5") is not deleted.

2.) If you had configured autostart for the old version, the corresponding "Startup" start menu entries are not removed.

3.) Several registry entries still point to the old LibreOffice installation. When you search the registry for "LibreOffice 3.5", you still find a bunch of according entries even after the update. You find even more when searching for "3.5" alone, but this will also yield some "false positive" entries that do not belong to LibreOffice.

While this is probably not a bid deal in practice, I like installers to be thorough. An uninstall should clean ANY AND ALL relicts of the application, and an update install should do the same for the respective old version.