AFAIK, this option is not available. I guess that so few people ever do this, that Adobe didn't think it was worth the effort to implement this.
Thanks Johan, appreciated.
I have a few clients requesting different sizes for their albums i.e. a large one for them and smaller ones for their families. I guess I've no choice but to start from scratch. Looks like my fee just went up!
Thanks for your reply,
I wanted to do the opposite, from standard landscape to large landscape. And I wanted to create a duplicate so I would not lose the version I had already published. What I found was that by right clicking on the book in the collection panel (in the Book module) there is a duplicate option. There is some tweaking required (resolution is poorer at the larger size, photo window sizing may need to be changed, etc.). But this seems to be exactly what I wanted without starting again, nor having to do too much rework.