The default font used for any of the text labels in either the key or any of the charts is set via the current Appearance stylesheet (see Editing a user Appearance stylesheet). If you have a particular font that you would always like to use for the text labels, then create an Appearance stylesheet and set it as the default stylesheet. This font is the one used when either a chart, column or row, etc. is created.
These fonts, though, can also easily be edited at any time.
To edit the font used by a label;-
Make a selection that contains all of the labels that you would like to reset. For example, if you wish to edit the font for all of the labels in a chart, then select the chart. This will include all of the row and column labels as well as the chart title. If you only wish to edit the font for some of the row labels in a particular chart, then select only those rows. Similarly, selecting the key will enable font editing for all of the key entries as well as the key title. Selecting a single key entry will enable font editing for only that key entry. If no selection is made, then all labels in all of the charts and in the key will have their font edited.
Select Edit > Edit Font from the main menu or select the Edit Font icon from the main toolbar..
The Font dialog opens allowing you to select any font installed on your system. You can change the font or the font style, size or colour.
Select the desired font.
Select OK. The labels within the current selection will be updated to the selected font.
Alternative sources of explanation: