If your intent is to “start over”, delete all of the pages, posts and media files on your site. Then, create new pages and posts.
Deleting a WordPress site is a non-recoverable action, which removes all of the content, uploaded information and the site itself. You will be able to login, but you won’t be able to do anything, because your site will be gone. This is hardly ever the desired choice.
Since deleting a site is a serious operation, you will be asked to confirm the decision. After confirmation, you will be sent a link in email that you must click to verify, again, that you truly want to remove all traces of the site. After clicking the confirmation link, the site will be removed. Make sure you really intend to remove the site completely and never use WordPress, again.