Text fonts are defined by several "text styles" that are specifically designed to give you polished presentations that work within each template.
To change the text font first select the text. Then from the drop down menu select the Text Style icon. You will have the option there of carefully selected style fonts labeled Title, Sub Title and Text that integrate into each of the templates seamlessly.
Once you have text box available on the slide, click on it. When you see the toolbar, click on the three dots on the far right side:
From here, you will see a white drop-down menu. Click on the menu and select the font of your choice: