When a site or subsite is no longer needed, such as one created for a completed project, you can delete it to free up space. To delete a site, team site, or subsite in Office 365 or SharePoint, you'll need Full Control permissions.
When you delete a site, you’re also deleting any subsites, content, and user information that are part of the site, including documents, document libraries, lists and list data.
Note: You need to have Full Control permissions to delete a site or subsite. If you don't have this level, talk to your site administrator or manager.
If you’re sure you want to delete the site, and you have the correct permissions, follow these instructions:
Navigate to the site or subsite you want to delete.
At the top of the site or subsite, click Settings and then click Site settings.
On the Site Settings page, under Site Actions, click Delete this site.
Note: If Delete this site doesn’t appear on the Site Settings page, you don’t have permission to delete this site.
On the Delete This Site page, verify that you are deleting the correct site, and then click Delete.
If you accidentally delete a site, it can be restored from the site collection recycle bin by a site collection administrator. See Restore an item from the Site Recycle Bin page.