Without reformatting and reinstalling everything....there is no safe way to truely remove all the old files. This is typical as a newer operating system overrides the older one and changes the MBR of the old to work with the new.

If there is a problem with any particular file then post about repairing or removal of that file...other than that I would leave things as they are ....you could be making it very bad on trying to remove the old system files.