[Theme: Flat 1.7.4] How to Make Dynamic Heading

Hello, how to make a dynamic heading in Flat 1.7.4 wordpress theme? I want to the site title to be H1 in homepage and H3 in single post.
The code is

echo '<h1 class="site-title ' . esc_attr( $header_class ) . '"><a href="' . esc_url( home_url( '/' ) ) . '" title="'. esc_attr( get_bloginfo( 'name', 'display' ) ) . '" rel="home">';

	if ( 'display-title' !== $header_class ) {
		echo '<img itemprop="primaryImageofPage" alt="' . esc_attr( get_bloginfo( 'name', 'display' ) ) . '" src="' . esc_attr( $logo ) . '" />';
	}
	if ( 'display-logo' !== $header_class ) {
		echo '<span itemprop="name">' . esc_attr( get_bloginfo( 'name' ) ) . '</span>';
	}

	echo '</a></h1>';