Did you even visit the link I posted? They tell exactly where to go and what to look for, all you have to do is read. Or watch the video. Remove sidebar by editing the php code – VIDEO
For example, in a typical WordPress theme you may need to edit index.php, page.php, single.php, archive.php, home.php and so on.
Open a template file to edit it and then locate the line that looks like this:
<?php get_sidebar(); ?>
If your theme comes with multiple sidebars, then you will see different instances of this code with a sidebar name inside the function. For example:
<?php get_sidebar('footer-widget-area'); ?>
Delete the line that represents the sidebar that you don’t want to display.
Now, save and upload the file back to your website. Repeat the process for all template files responsible for displaying different pages on your website.
Once finished, you can go to your website and see it in action.