There are legend titles for the entire legend, for the color of the regions, for the color of the points, and for the size of the points.
If the legend title is not showing, click the legend icon . In the General section
of the Properties pane, set the Legend
Title to Show.
In the report, double-click the legend title and type the title.
By default the legend titles are taken from the object you've selected from the data source. To change a title, do one of the following:
In the Insertable Objects pane, drag a text or calculation object to the Color Legend Title drop zone in the Region Layer or Point Layer, or the Size Legend Title drop zone in the Point Layer.
Double-click the Color Legend Title or Size Legend Title drop zone, to change from the default legend title, then double-click the drop zone again. In the Text dialog box, type text for the legend title.