Danger Zone

In the "General" ("Site Settings") panel, you'll find the "Danger Zone" tab on the top menu. In this screen, you can perform site-wide actions that cannot be reverted, so please continue with care!

You can reset all the default site options/settings back to default, delete all of the site custom content (pages and blog posts) or delete the entire site if you want to start from scratch or no longer need it -