The Graph item can have one or more titles. By default the graph item have one title with TopCenter Position.
To add title:
Click the graph that you want to change.
The selected graph properties are listed in the Property Browser.
In the Titles property, click the Edit Collection (…) button. The GraphTitle Collection Editor opens.
Click Add to add a title and set the Text property.
Click Add to add more colors to the palette.
When you are done, click OK.
Changing the title:
Click the graph title that you want to change.
The selected title properties are listed in the Property Browser.
Alter the title properties according to your requirements.