[Savannah-hackers-public] Is is allowed to replace GPL2+ license notices?

[Sebastian Gerhardt]

Hi there,

sometimes they are projects that are licensed as a whole under GPL3+ but
contain some single files written by other authors under GPL2+.

The new maintainer is entitled to redistribute all files under GPL3+,
but is it legal and lawful for him to simply replace the old GPL2+
notice with the GPL3+ as to improve consistency? Or must they be
preserved?

Regards
Sebastian