Changing title heading category

Hi,
I’m working on this website : http://www.dorotheewierez.fr
I’m usigne the slideshow in the main page. There is a lot of picture and the title of each picture is read as a <h2> category. I would like to bring it in the <h3> category. Where can I change this setting to make each title of picture read as h3 instead of h2 ?
Best regards,

http://ww.wp.xz.cn/plugins/slideshow-jquery-image-gallery/