https://bugzilla.redhat.com/show_bug.cgi?id=1344276
--- Comment #35 from Paulo Andrade paulo.cesar.pereira.de.andrade@gmail.com --- The easiest approach would be to make a new release, and change the files to use GPLv3+. But you would need to ask all contributors to agree to it. Likely just one line replacement of /2/3/ for the files under GPLv2+.
Files without a license header use the LICENSE file. But IANAL, and this could be contested. But I do not suggest patching the files to add a license header, as most if not all are kind of trivial or non distributed files.