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This is Jonis from Microsoft SharePoint Online Support.
To delete or change the zones on your SharePoint Online public-facing website, use the Office 365 web design tool layout ribbon option.
From your Website select the Web Page Home to open the Office 365 Web Design Tool. On the Web Design Tool ribbon select the Design tab and use the Layout dropdown to change the zones.
The following link contains a number of articles detailing how-to design a public-facing website in SharePoint Online: Designing a public-facing website
If that does not answer your question please let me know as I will continue to monitor this thread for a few days and will reply to any additional posts or questions.
Microsoft Office 365 SharePoint Support