Deleting a site permanently removes it, along with its files, database, and backups. This cannot be undone, so save anything you need first.
Find the site's actions
Open the site you want to delete. Its action buttons, including More, sit in the top right of the page.
Delete the site
Click More, then choose Delete Site.
Read the warning in the confirmation window.
Click Delete to permanently remove the site.
To take a site offline for a while instead of removing it, suspend it (see Suspending and reactivating a site).