If you want to change the default font used in any PowerPoint template then this simple trick can be helpful. First, you need to access the Slide Master view under View menu. Then, look for the layout where you want to change the default font and for each layout choose the new font to be used.
Right click on the text level where you want to change the font and then click on Font… option. Now you can choose the font face to use and font properties. This will apply for the template or will help you to change the default font in powerpoint 2010 or 2013.