A map legend in a Layout window is made up of individual legend frames that are each unique to a layer on the map. To customize your map legend, you would edit the contents of the legend frames to support the design of the final map and to clearly communicate the map contents to the reader.
Each legend frame may have a title and subtitle. You can edit the label text, change the font size and style, and change the sample size. You also have control over how to sort the labels.
To edit the contents and display of a legend frame:
To have more than one column in a legend frame, either set the number of columns in the Legend Frame Properties dialog box or resize the legend frame.
To modify how a thematic legend displays, right-click on it and select Modify Legend's Thematic Map to open the Modify Thematic Map dialog box. You can then customize the display properties of the thematic map legend. This option is only available on a thematic map legend frame.