If you draw a shape on your page and want to convert it quickly to another shape, use the options in the Object, Convert Shapes submenu. You can convert the selected shape into any of the following:
Inverse Rounded Rectangle
Polygon (if you choose this option, it defaults to the last type of polygon you specified. If you have a certain shape in mind, double-click on the Polygon tool in the Tools palette to open the Polygon Settings dialog and enter specifics about the number of sides and star inset before you choose this menu option).