Go to your organization page.

First, check if all the opportunities are deleted, also in the archive.

If an opportunity is closed or expired you need to open or extend it before being able to delete it.

Go to the "Settings" tab. See here:

Then press the "Customize" tab.

At the bottom of the page, you will find a button “Delete organization”.

Press the red button.

Type the name of your organization, ensure there are no spelling mistakes, and press the red button again.

Your organization will now be deleted. It is possible that you will still be able to view the organization as it will only be gone once our database is updated.