License change from GPL to AGPL

Here is an extract of replay from the FSF (http://www.fsf.org/) concerning license changes

>> At which condition can an editor (owning copyright) change the license  from GPL to AGPL?


"The copyright holder on a work always has the option of relicensing that work under any terms they choose. Keep in mind, however, that previously released copies of the work would still be under the original license, and anyone who has a copy can continue to modify, copy, and redistribute from their copy under that older license. Thanks once again for your interest, and I hope this helps."