I upgraded from Photoshop CS5 to CS6, and from Lightroom 3 to 5. Do I have to keep any of the files from the previous version?
At least in PS if you uninstall old versions you can run into file association problelms. Best advice is to leave as is unless you really need the disk space.
And if you uninstall, I believe that plugin folders etc will not be removed, but as Surt says, always best to leave the old version installed at least for a while. It might be that certain plugins, or twain drivers etc will not work on later versions, or will be problematic.