Most Cortex case presenters allow for changing font size using the font sizing buttons typically located above the text areas.

Some areas like the Cortex advanced area do not have font sizing functionality and in these situations you may want to adjust the font size for your browser or use zooming functionality to enlarge the text. The easiest way to enlarge what you are seeing is by holding down the Control (PC) or Command (Mac) key and then using the +- keys on your keyboard to enlarge or reduce.  An alternate method is to hold down the Control or Command key and then use the scroll wheel on your mouse.

How to customize the font size and additional information can be found here.