You want your disk space back. As an experienced veteran of the disk space wars, you know better than to delete the folder that the application is installed in. You go instead in search of the uninstall utility for that application. You find it. You run it.
Uninstall routines can leave little bits and pieces behind.
Usually these will be found in the Windows registry or some other data file that is shared by other applications. This is a major problem. Luckily Microsoft, in Windows ME, finally addressed the problem by creating the restore utility which can help in correcting the error. But there are times when even that wonder can't help. Restore depends on dates and many of us can't remember when we install things.