widget titles from H2 to h4

Dear team,

In my online casino site, I wish to change all the widget titles from H2 to h4.

In which file can I change them H2 to h4?

<section id="image-3" class="widget widget_image">
   <div class="widget-wrap">
     <h2 class="widget-title">WIDGET NAME</h2>

Thanks, Offir