how to change the size of the full name quick tool?

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

Example:

#id_5 {

    font-size: 25px;

}

Let us know if you need more help, we will be glad to assist you.