You can’t unpublish your website.
You will need to delete it if you want it to go offline. Note, however, that all of your content will be lost if you delete a website.
If you want to keep a copy of the contents of the website but not have it live, do this:
1. In your Dashboard, hover over the thumbnail of the website that you wish to unpublish and click on the settings wheel.
2. Click on Duplicate site. You will then have two versions of your website, a published one and a not published one.
3. Delete the original website that you wanted to unpublish.