scaling staff sizes

I've finished the piece I was working on - SATB a capella - then used the advice I got to create a piano reduction on the bottom.

Of course, now each system is so high that it only fits one on a page.

I can go back and compact the space between staves in each system, and that might give me the space I need to put 2 systems on a page, but I'm wondering if there's an easy way to scale the whole file to (say) 90% - in which case it will probably fit 2 per page.

Just asking.

Roger.