Final answer:
The best way to change the font size of all notes pages at once is by using the Notes Master, which allows you to make changes that apply to all notes in the presentation.
Step-by-step explanation:
The best way to change the font size of all your notes pages at once in a presentation software such as Microsoft PowerPoint is by using the Notes Master. The Notes Master is a feature that allows for formatting and style changes to be applied to all notes pages simultaneously.
To use this feature, you typically go to the 'View' tab, select 'Notes Master', and then make the necessary changes to the font size. Once you've made your changes, they will apply to all notes associated with your slides.