Select legend > Editor > Edit Legend > Header Font
After creating a graph, you can change the legend title font or its attributes.
Font: Enter a font type.
Style
Bold: Check to make the text bold.
Italic: Check to italicize the text.
Underline: Check to underline the text.
Size: Enter a font size.
Color: Choose a text color.
Preview: Displays sample text with the selected attributes applied. This box does not accept input.