add_filter( 'iworks_upprev_box', 'iworks_upprev_box_mycontent' );
 
function iworks_upprev_box_mycontent( $content )
{
    $value = '<div id="upprev_box">';
    $value .= '<h6>My own title</h6>';
    $value .= '<div class="upprev_excerpt">';
    $value .= '<h5>Lorem ipsum</h5>';
    $value .= '<p>Lorem ipsum dolor sit amet, consectetur ';
    $value .= 'adipiscing elit. Vestibulum auctor neque vitae orci ';
    $value .= 'ornare et vehicula eros molestie.</p>';
    $value .= '</div>';
    $value .= sprintf(
        '<a id="upprev_close" href="#" rel="close">%s</a>',
        __('Close', 'upprev')
    );
    $value .= '</div>';
    return $value;
}