You have a few options.
To remove the sidebar everywhere, add this to your custom CSS:
#sidebar {
display: none;
}
You may then want to adjust the widths of elements in your main column to fill the space left by the missing sidebar, which you can do with CSS.
Don’t edit the theme files directly, otherwise your changes will be overwritten whenever the theme is updated.
An easy way to add custom CSS is to install the Jetpack plugin and activate the Custom CSS module. You’ll then add your custom CSS in the new stylesheet editor that’ll appear in your dashboard, under Appearance > Edit CSS.
As alternatives, you could either install a standalone custom CSS plugin, or create a child theme.
If you didn’t want to remove the sidebar everywhere, but instead wanted to create a full-width template that you can select only on specific pages, it’s a little more complicated. You’d first need to create a child theme, and then build a new custom page template which removes the call to the sidebar.
Hope this points you in the right direction. If you’re not comfortable making a few code changes with some guidance, then choosing a different theme that does include a full-width page template may be an easier route.
