[JKT]

The same thing as Joel has written applies. However, if the shape/object you want to swap for is only on the stencil and not on the canvas, and it isn't one of the standard shapes, it won't appear as a shape in the Lines and Shapes canvas. The solution is to simply drag and drop the alternative shape to your canvas, it will then appear in the inspector and you can then swap the old shape for your alternative one. Then you can delete the one you drag and dropped to clear it from your diagram.