How to Delete or Retire a SharePoint Site.

As a site collection admin/owner you can delete your site at any time.  Here are the steps.  This will delete all content in the site collection include any subsites.  

1. From the home page of the site click on the gear in the upper right hand corner and select "Site information"
2. Click "View all site settings"
3. Click "Delete this site".  
4. Click the "Delete" button.  

Remember this deletes the parent site as well as any subsites under the site.  The site will go to the "Deleted sites" area in the SharePoint admin center where the site collection can be restored by a SharePoint central admin up to 93 after it is deleted. 

Note: SharePoint sites connected to a Microsoft Team must be deleted with the Microsoft Team from the Teams client.  When the Microsoft Team is deleted the corresponding SharePoint site will also be deleted.  You cannot delete a SharePoint site connected to a Microsoft Team you must delete both the Team and the SharePoint site.