How can I increase the font size of my sub labels on a registration form?

Is this your form in question? http://www.jotform.co/form/81937346101858 

Please try injecting the following CSS code: https://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes 

.form-sub-label {

    font-size: 14px !importatn;

}

Let us know if you need more help.