You may want to replace an existing font on all slides with a different font. E.g., the headings on all slides are Arial. You want to replace the font style with Bookman Old Style. To manually change the font of all instances of the text will be tedious and time-consuming. PowerPoint enables you to change all instances of the font at the same time. Steps to replace fonts:
Select Format àReplace Fonts command (Replace Font dialog box is displayed)