Click the Change To button on the Diagram toolbar.
Click a new style.
PowerPoint applies the style.
If you added a diagram to your slide, you can swap diagram styles at any time. Using the Diagram toolbar, you can assign another diagram style without affecting any data you have previously entered into the diagram.
Changing Text Formatting
To assign another font to your diagram text, simply select the text and click the down arrow next to the Font button on the Formatting toolbar to choose another font style.
The diagram style you should choose depends on the order in which you want to present the diagram flow. For example, a cycle diagram shows continuous flow in a circular pattern, while a radial diagram shows outward flow from one source.