The font size used throughout Project Insight sets the size of the most common font within the interface and scales the other sizes, both smaller and larger, proportionally. Padding between lines will also increase or decrease with the size change.
To change the font, from the deafult, click the drop down and select a size.
This is an example of the Largest (16px):
This is an example of the Smallest (11px):
To set it back to the default size, click the No Selection or Normal (13px) - Default option.