change font style

If I understood you correctly you want to change form font. Inside of this guide you can find how to do it: http://www.jotform.com/help/185-How-to-Change-Form-Fonts

You can also use Google fonts in your form: 

http://www.jotform.com/help/100-How-to-Use-Google-Fonts-in-your-Form 

In case that you want to change font color, you can do it inside of Form Designer. Inside of Form Designer select Color Scheme tab. There you can change color of text inside of your form.

Hope this will help. Let us know if you need further assistance.