Increasing font size on only one field?

Hello markring,

First, you need to identify the class or ID of the field you'd like to increase. Next, you can add a CSS code that will make the font size increase on that specific field.  Next, you can inject the CSS code in to your form, this user guide will help you how to do CSS injection. 

But to be able to help you further in detail, may I request the link to the form and also which part of the form is it that you wish to adjust its size? 

Thanks.