If you want to delete a plan, click on the gear wheel in the basic settings to open the configuration options and choose Delete Plan:
As a plan includes several important information such as versions, policies and change logs, you will have to confirm, that you really want to delete the plan including all its elements.
Please read the confirmation dialog carefully.
The button to delete the plan will only be enabled if you enter the correct name of the plan in question:
You cannot delete a plan that has already been locked. Locked plans will be deleted only if the complete organization is deleted.