Double-click on an axis to open the Format Axes dialog. Or click on the Format Axis tool in the Prism toolbar.
Prism chooses the range of each axis automatically. To override this, uncheck the "Automatically determine the range and interval" box and enter the minimum and maximum value you want plotted on the axis. You can also hook a range limit to an info constant.
You can only set the range on numerical axes, not the categorical axis of Column and Grouped graphs.