number of systems per page

[Carlos Garcia Suarez]

I am about to finish transcription of a Bach piece for piano. It looks nice except that I only have 5 systems (i.e. pair of cleff and bass staffs) in each page, and I would like to have 6. How can make them fit? How do I reduce the inter system spacing to allow for one additional system in each page?   Responses via email would be much appreciatted   Carlos Madrid