Click on the arrow icon beside your project name, and select Delete from More.
Note: Only an admin of the organization would be able to delete it.
The deleted organization will be found in the trash bin at the sidebar. You will be able to restore the deleted organizations within 7 days. After 7 days, the organizations will be deleted permanently.
Note: The deleted organization will not be counted towards the organization limitation (35) per account. However, you will not be able to restore a deleted organization when your active organization has already hit the limit.