If you're really confident that there won't be any bugs in the new version and if you don't have a whole lot of existing programs that you have to maintain, then go ahead and uninstall your old version first. I prefer to keep it safe and do a slower, planned transition with a new release. Once upon a time, LabVIEW did install to a common directory and most users didn't like that. NI listened to the complaints and changed the behavior of the installer. I much prefer the current method.
