Most of the time, SmartArt graphics work great with their default looks — and that’s something to credit Microsoft with. In addition you can change one SmartArt graphics to another and you can also change colors or apply a new SmartArt Style to make your SmartArt appear distinct and unique. What many users don’t realize though is that they can change the individual shapes within a SmartArt graphic to another shape — for instance, you can change some circles in your SmartArt graphic to squares with a mere click or two!
Learn how to change shapes within a SmartArt graphic in PowerPoint 2011 for Mac.

