Delete a site collection
When you, as a global or SharePoint admin in Office 365, delete a site collection, it's moved to the site collection Recycle Bin and retained for 93 days. Deleting the site collection deletes everything within it, including:
Document libraries and files.
Lists and list data.
Site settings and history.
Any subsites and their contents.
You should notify the site collection owners and subsite owners before you delete a site collection so they can move their data to another location, and also tell users when the sites will be deleted.
To delete a communication site or a team site that uses one of the new templates, use the new SharePoint admin center preview. For info, see Manage sites in the new SharePoint admin center.
Delete a site collection in the classic SharePoint admin center
Sign in to https://admin.microsoft.com as a global or SharePoint admin. (If you see a message that you don't have permission to access the page, you don't have Office 365 administrator permissions in your organization.)
In the left pane, select Admin centers > SharePoint. If this opens the new SharePoint admin center, select Classic SharePoint admin center in the left pane.
Select the check box next to the site collection or multiple site collections that you want to delete.
On the Site Collections tab, select Delete.
Confirm the information in the Delete Site Collections dialog box, and then select Delete.