To delete a space:
Log into the web app.
In the top-left of the navigation bar, click the organization name, then click "Organization settings".
You'll be brought to the Subscription overview page. You'll see an overview of the space(s) belonging to your organization. Click on the three-dotted icon on the right side of the space you want to remove, and select "Delete".
NOTE: All content in the space will be deleted. Make sure to backup your data using Contentful CLI tool for data exporting.