I have NetBeans IDE 6.9 installed on my Windows XP machine. If I use
Help -> Check for Updates it doesn't detect a new version, but the NetBeans web site lists 6.9.1 as the latest release.
I downloaded the 6.9.1 installer, but if I try to select the same folder as my existing install for the destination it won't allow me, telling me the folder isn't empty.
The FAQ gives an example of an upgrade that can't be accomplished, but shows a major release version difference, not a minor one.