One of the most powerful features of Crystal is the ability to Group data.
And once you have some summaries working for you, groups, then, become synonymous with Dimensions. Think pivot tables.
It is a very common thing to change the dimensions of a report.
In Crystal, select Report | Change Group Expert.
From here, you can select a Group and use the arrow [mouse] buttons to change the "level" of the Group.
Clicking "Options" will allow you to change the Group Field, effectively picking a different dimension.