Resizing layout parts
2. Do one of the following:
•Drag the part label or part boundary (the line that marks the bottom of the part) until the part is the height you want.
•To maintain the height of the entire layout while changing the size of one layout part, Alt-drag (Windows) or Option-drag (macOS) the part label or part boundary. (This causes the size of the layout part immediately below the part you're changing to also change.)
•To precisely resize a part, select the part by clicking its part label. Click
Inspector 
in the
layout bar, then click the
Position 
tab. Enter a value for the part's
Height or
Bottom boundary in the Position area. See
Using the Inspector to position objects.
You can also use the rulers, grid, and guides (choose
View menu >
Rulers,
View menu >
Grid >
Show Grid, and
View menu >
Show Guides) to help with precisely sizing parts. See
Using the rulers and grid and
Using guides and dynamic guides.
in the