You can change the font and font size of text and replace a font everywhere it occurs in your presentation.
Select the text you want to change.
To change all of the text in a text box or a table cell, select the text box or triple-click the table cell.
Click the Text tab at the top of the sidebar on the right, then click the Style button near the top of the sidebar.
If you don’t see a sidebar, or the sidebar doesn’t have a Text tab, click 
in the toolbar.
Click the Font pop-up menu, then choose a font.
Click the small arrows to the right of the font size to make the font larger or smaller.
To change a font everywhere it occurs in your presentation, you can replace it with another font.
Choose Format > Font > Replace Fonts (from the Format menu at the top of the screen).
Click the double arrows to the right of the font you want to replace, then choose a replacement.
If the font is listed as a missing font, also choose a typeface.
Click Replace Fonts.
The font is replaced everywhere it occurs. The replacement font uses the same size and weight as the font it replaces.
If you have the missing font and want to install it on your computer, use Font Book, available in the Applications folder of your Mac. For more information, see Install and view fonts in Font Book Help.
If you chose a replacement font for the presentation then installed the missing font, your presentation continues to use the replacement font unless you replace it again with the font you installed.
Tip: You can add buttons to the toolbar for changing the font and making selected text bigger or smaller.