How to delete a stage:
Path: Community Settings >> Workflow >> Funnel Management >> Edit (Funnel)
Community Administrators can delete a stage from the funnel management area.
If the stage contains even one idea, then the delete option will not be visible to the Administrators. In order to delete a particular stage all ideas in that stage needs to be moved to another stage.
How to delete a funnel:
Path: Community Settings >> Workflow >> Funnel Management >> Delete
Community Administrators can delete an entire funnel permanently.
Community Administrators cannot delete a funnel if there are ideas in the funnel and if the stage is being used for any other assigned Campaigns. In this scenario you could either move all the ideas and campaigns to a different funnel.