Scale the Chart
You can
edit the height and width independently. Here is a method for
keeping a fixed aspect ratio: changing both sides the same percent.
Try it: Scale the Chart
Select the
chart.
Go to
PivotTable Tools.
Look for
Format->Size.
What Do
You See? At the corner of the Size group
you can see a small arrow. Click on the arrow to get to the
advanced options.

Size and Scale: Adjust the
Scale from 100% to 75%.