Editing components
When you select a Component on the canvas, you'll see two Component properties in the Property Inspector: Break Apart and Edit Source.
Break Apart breaks the connection between the individual UI elements inside the Component and the Component itself for the selected instance, meaning that it is no longer a Component (although the original Component remains intact). Any changes you make to a broken apart Component will not get updated elsewhere and any changes made to the Component will not update where it has been broken apart.
Edit Source takes you to the Components editing mode where you can edit the Component. The main benefit of reusable Components is that if you need to make a change, you can just do it in one place and it will be propagated to all the instances (uses) of that Component. When you are done editing a Component, you can click the "Done" button on the canvas. Edits made to the Component will be immediately reflected in any wireframes using it.