What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
There are various ways to do it:
1) You can change the font size of your form by using the Form Designer tool: http://www.jotform.com/form-designer/tuts/episode2/
2) Also, you can do it from Preferences:
3) If you want to change the size specifically to a field, you can do it through CSS injection: http://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes
Let us know if you need more help, we will be glad to assist you.