Changes to a chart/plot can be made by clicking an open area of the chart
with the right mouse button. You have many options in the window given.
For example,
Other changes can be made to the appearance be selecting Format Chart Area.
Note:
A similar process can be followed to make changes to other parts of the chart. Simply place the cursor over the object to be changed, click the left mouse button. Clicking the right mouse button gives a menu of options.