Header change

Open header.php and delete these lines:

<nav class="menu-wrap<?php ac_mini_disabled(); if ( get_theme_mod( 'ac_disable_stickymenu' ) ) { echo ' sticky-disabled'; } ?>" role="navigation">
		<?php
			if( has_nav_menu( 'main' ) ) {
				wp_nav_menu( array( 'container' => '', 'theme_location' => 'main', 'items_wrap' => '<ul class="menu-main mobile-menu superfish">%3$s</ul>' ) );
			} else {
				echo '<ul class="menu-main mobile-menu superfish"><li class="current_page_item"><a>' . __( 'Add a menu', 'acosmin' )  . '</a></li></ul>';
			}
		?>

        <a href="#" class="mobile-menu-button"><?php ac_icon( 'bars' ) ?></a>
        <?php if ( !get_theme_mod( 'ac_disable_minisidebar' ) ) { ?>
        <a href="#" class="browse-more" id="browse-more"><?php echo ac_icon('caret-down', false) . __( 'Browse', 'acosmin' ) ?></a>
        <?php } ?>
        <a href="#" class="search-button"><?php ac_icon( 'search' ) ?></a>

        <ul class="header-social-icons clearfix">
			<?php
				// Social variables - Options Panel
				$header_fb 	= of_get_option( 'ac_facebook_url' );
				$header_tw 	= of_get_option( 'ac_twitter_username' );
				$header_gp 	= of_get_option( 'ac_gplus_url' );
				$header_rss = of_get_option( 'ac_custom_rss_url' );

			?>
			<?php if ( $header_tw != '' ) { ?><li><a href="https://twitter.com/<?php echo esc_html( $header_tw ); ?>" class="social-btn left twitter"><?php ac_icon('twitter'); ?></a></li><?php } ?>
			<?php if ( $header_fb != '' ) { ?><li><a href="<?php echo esc_url( $header_fb ); ?>" class="social-btn right facebook"><?php ac_icon('facebook'); ?></a></li><?php } ?>
			<?php if ( $header_gp != '' ) { ?><li><a href="<?php echo esc_url( $header_gp ); ?>" class="social-btn left google-plus"><?php ac_icon('google-plus'); ?></a></li><?php } ?>
			<li><a href="<?php if( $header_rss != '' ) { echo esc_url( $header_rss ); } else { bloginfo( 'rss2_url' ); } ?>" class="social-btn right rss"><?php ac_icon('rss'); ?></a></li>
        </ul><!-- END .header-social-icons -->

        <div class="search-wrap nobs">
        	<form role="search" id="header-search" method="get" class="search-form" action="<?php echo esc_url( home_url( '/' ) ); ?>">
            	<input type="submit" class="search-submit" value="<?php _e( 'Search', 'acosmin' ); ?>" />
            	<div class="field-wrap">
					<input type="search" class="search-field" placeholder="<?php _e( 'type your keywords ...', 'acosmin' ); ?>" value="<?php get_search_query(); ?>" name="s" title="<?php _e( 'Search for:', 'acosmin' ); ?>" />
				</div>
			</form>
        </div><!-- END .search-wrap -->

    </nav><!-- END .menu-wrap -->

Then open style.css and find:

.top {
     height: 150px;
}

Change it with:

.top {
     height: 220px;
}

Then go in your WordPress Adminitration Panel, then Appearance and select Editor. You will find the files on the right side, open them and change them as I said above.

You can open style.css, find:

.logo {
display: inline-block !important;
position: absolute;
font-size: 36px;
letter-spacing: 10px;
font-weight: normal;
text-transform: uppercase;
text-align: left;
top: 50%;
left: 35px;
transform: translateY(-50%);
}

replace with:

.logo {
display: inline-block !important;
position: absolute;
font-size: 36px;
letter-spacing: 10px;
font-weight: normal;
text-transform: uppercase;
text-align: left;
top: 50%;
left: 50%;
margin-left: -245px;
transform: translate(0, -50%);
}