Double click within the Annotation box to edit the chart. You can tell the chart is in the edit mode when a blue border appears. Clicking outside of this border will take the chart out of edit mode.
While editing the chart you can select chart components with the Chart Annotation and move or resize them as desired. To resize a chart and all of its interior components, right click on the Chart Annotation and select Automatic Resizing from the menu. Now, when you grab a point on the Annotation and drag it for resizing, the contents of the Chart Annotation resize with it.
You can also add components to a chart while in edit mode. The components are added just like you would add them to a page. Select the corresponding button, for the annotation you want to add, and draw it inside the chart's border. The annotation that you can insert into a chart are lines, shapes, tables, text and plot spaces.