This option is only available for blank designs/fully editable templates
When three or more panels are selected followed by Distribute Panels from the Modify Panel toolbar, a sub menu will appear providing vertical and horizontal distribution options.
The options vertically or horizontally justify the space between the selected panels.
As panels may be different dimensions, the distribute tool uses the centre of the panels to define the distance between them.
Selecting Distribute Vertically will distribute the spacing between the three shapes vertically, making the spacing equal.