Choose Pages > Settings (from the Pages menu at the top of your screen).
Click General, then select the checkbox next to “Set font and size for new Basic documents.”
Click the Font pop-up menu and choose a font.
Click the arrows next to Font Size to choose a font size, or type a value in the text field.
Click OK.
After you make the update to the setting, it applies to any new documents; it doesn’t change the font for existing documents. If you later want to revert the templates to their original fonts, deselect the “Set font and size for new documents” checkbox.
Go to the Pages app
Click the paragraph style at the top of the sidebar (in the example above, it’s Title), then choose the style you want to modify.
Tip: You don’t have to modify every paragraph style in the template; for example, for a simple letter or document, you may want to modify only the body text style and a heading style.
In the Font section of the sidebar, choose a font and font size for the paragraph style you selected.
You can also use other controls in the Font section to choose character styles like bold and italic, and change the text color.
Update the paragraph style with your changes:
If there’s an Update button: Click Update.
If there’s only an asterisk next to the paragraph style: Click the style name, then move the pointer over the style name in the Paragraph Styles pop-up menu. Click the arrow that appears, then choose Redefine from Selection.
You can Intro to paragraph styles in Pages on MacChange the font or font size in Pages on Mac