<DomainName> can't be removed because you're using it for your SharePoint Online website. If you want to remove the domain, first change the address that you're using for SharePoint Online to a different domain.
- Sign in to the Office 365 portal (https://portal.office.com) as a global administrator.
- Click Admin, and then click SharePoint.
- On the Site Collections page, click to select the check box next to your public website link, and then click Rename Website.
- In the list, select <your_domain>.sharepoint.com, and then click OK.
- Wait 1 hour, and then try to remove the domain. Check back periodically. The process could take as long as 24 hours.
Article ID: 2787264 - Last Review: Dec 28, 2016 - Revision: 1