Select Page from the Display menu. Click on the Set button for Staff Spacing to bring up the Staff Spacing dialog.
You can move the staves that appear on the window on the left side of the Staff Spacing dialog by dragging them up or down. You can move the staves three different ways, depending on the moving mode you select. If you choose Independent, moving a staff up or down does not affect any of the other staves. If you choose Accordion, the top staff and the bottom staff are anchored and the staff you move pulls the staves above and below it in an accordion effect. Choosing Push Up/Down moves the staves below the one being moved, along with the one being moved, as you move it up or down. If you click on the Default Spacing button the staff spacing will revert to the default. Of course, if you have only one track in your piece, you won't be able to affect the spacing between staves.
You can affect the spacing between systems by setting a new value in the System Spacing list box. By default, the spacing between systems is set at 4, which is about equivalent to the space between three ledger lines. This means that systems are spaced apart by this amount in addition to the default spacing between staves in the same system.