Sometimes an idea starts one way and transforms into something else. To help, you can switch object types easily on the canvas. Let's say you added a shape but realize it'd be better suited as a sticky note. You can do that!
To switch object types:
Click on the object (a sticky note, shape, paragraph, etc.) you want to change to something else.
Click the Switch type icon in the toolbar.
Select a new object type.
And voilà! You've switched to a new object type.