Click a data series in the pie chart you want to change.
On the Format menu, click Selected Data Series, and then click the Options tab.
In the Size of second plot box, enter a value between 5 and 200 to specify the size of the second pie or bar as a percentage of the first pie chart. For example, 105 makes the second pie or bar 5 percent larger than the first.
Change the size of the pie-of-pie or bar-of-pie plot area