I have a Flash project, and it has many source files. I have a fairly heavily-used class, call it Jenine. I recently (and, perhaps, callously) relocated Jenine from one name
Flash still has the ASO file, which is the compiled byte code for your classes. On Windows, you can see the ASO files here:
C:\Documents and Settings\username\Local Settings\Application Data\Adobe\Flash CS4\en\Configuration\Classes\aso
On a Mac, the directory structure is similar in /Users/username/Library/Application Support/
You can remove those files by hand, or in Flash you can select Control->Delete ASO files to remove them.