Remove side Bar from specific pages

You can create a Page Template for this purpose, create a new file called template-full.php and place it within your Child Theme folder.

Add this to the template-full.php file:

<?php
/* Template Name: Full Width */
get_header(); ?>
<div id="primary" class="content-area">
    <main id="main" class="site-main athena-page" role="main"><?php 
        while (have_posts()) : the_post(); 
            get_template_part('template-parts/content', 'page-full'); 
            if (comments_open() || get_comments_number()) :
                comments_template();
            endif; 
        endwhile; ?>
    </main> 
</div><?php 
get_footer(); ?>

Create a sub-folder within your child theme folder called template-parts, and create a new file inside it called content-page-full.php.

Add this to the content-page-full.php file:

<?php if (get_post_thumbnail_id($post->ID)) : ?>
    <div id="athena-page-jumbotron" class="parallax-window" data-parallax="scroll" data-image-src="<?php echo wp_get_attachment_url(get_post_thumbnail_id($post->ID)) ?>">
        <header class="entry-header"><?php 
            the_title('<h1 class="entry-title">', '</h1>'); ?>
        </header>
    </div><?php 
endif; ?>
<div class="row">
    <div class="col-sm-12">
        <article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
            <div class="entry-content"><?php 
                if (!get_post_thumbnail_id($post->ID)) : ?>
                    <header class="entry-header"><?php 
                        the_title('<h1 class="entry-title">', '</h1>'); ?>
                    </header><?php 
                endif;
                the_content(); 
                wp_link_pages(array('before' => '<div class="page-links">' . esc_html__('Pages:', 'athena'),'after' => '</div>',)); ?>
            </div>
            <footer class="entry-footer"><?php
                edit_post_link(sprintf(esc_html__('Edit %s', 'athena'), the_title('<span class="screen-reader-text">"', '"</span>', false)), '<span class="edit-link">', '</span>'); ?>
            </footer>
        </article>
    </div>
</div>

You can now edit a page and assign the new page template you’ve just created to it, it should display full-width with no sidebars.

All of the above code has been taken from the existing theme files with very minor modifications to load a different content file and to remove the sidebars.

Hope this helps.