for p_h in Page.versions.filter(version_info__user=other_matt):
    p_h.history_user = matt  #Have to set using the direct "history_user" attribute rather than p_h.version_info.user (which doesn't allow mutation)
    p_h.save()

other_matt_profile = UserProfile.objects.get(user=other_matt)
other_matt_profile.delete()
other_matt.delete()