Once a shape has been added to the page, you can edit it to make further changes. If the shape is pre-defined you'll first need to make the shape editable by choosing Format->Make Shape Editable. This causes editing handles to appear, allowing you to make adjustments:
Note: Closed shapes must have at least three points—you will be unable to delete points when there are only three remaining.
To convert a shape with sharp edges to one with a smooth, rounded outline choose Format->Smooth Path:
To convert a shape with a rounded outline to one with sharp edges choose Format->Sharpen Path:
Note:Pre-defined shapes must be made editable (with Format->Make Shape Editable) before they can be smoothed or sharpened.