[bayes]

If you own the copyright to the whole project (because all the other contributors assigned copyright in their contributions to you) you can presumably distribute it under any licence you want. But you can't prevent other people continuing to distribute it under the GPL.

If (as seems more likely) the other contributors still hold the copyright to their own contributions, your only rights to their code are those granted under the GPL, so you couldn't distribute it under any other terms.

At any rate, those are my thoughts, but IANAL.