How to change h1 to h2 in page title

Hi guys.
I have the same problem as the guy wrote in this post. -https://www.ads-software.com/support/topic/how-to-change-page-title-to-h2-tag?replies=3 , but the thing is that solution want work for my theme.

Here’s the pic of what I want to change:
https://www.dropbox.com/s/zpbmydvcupj85h0/h%20tags.png?dl=0

I want to change page titles (in this pic “O agenciji”) from h1 to h2, because SEO.
Maybe is okay to leave it like that so both(site title and page title) are h1, and that want take much affect on SEO, but just want to change.

Here is my code in content.php
`<header class=”entry-header”>
<div class=”entry-meta”>
<?php sequential_entry_meta(); ?>
</div><!– .entry-meta –>

<?php the_title( sprintf( ‘<h2 class=”entry-title”>‘, esc_url( sequential_get_link_url() ) ), ‘</h2>’ ); ?>
</header><!– .entry-header –>

<div class=”entry-content”>
<?php
if ( ! is_search() ) {
the_content( __( ‘Continue reading <span class=”meta-nav”>→</span>’, ‘sequential’ ) );
wp_link_pages( array(
‘before’ => ‘<div class=”page-links”><span class=”page-links-title”>’ . __( ‘Pages:’, ‘sequential’ ) . ‘</span>’,
‘after’ => ‘</div>’,
‘link_before’ => ‘<span>’,
‘link_after’ => ‘</span>’,
) );
} else {
the_excerpt();
}
?>
</div><!– .entry-content –>
</article><!– #post-## –>

It want work?
Or should leave it like it is? (I’m little bit SEO sceptic) because this w3c analyze. – https://validator.w3.org/nu/?doc=http%3A%2F%2Fastrazlata.rs%2Fo-agenciji%2F on line 10