Deleting a process in some cases requires additional actions before you are able to delete it. If process flow is setup between this process and another you will need to delete the process flow first. If there are reference fields to different processes in this process, you will need to delete those reference fields first. 

We do not recommend deleting a process unless absolutely necessary. Instead, we recommend Archiving the Process. 

Top Menu >> Setup >> Select the Process. 

Under the More menu, click Delete.

The examples below are the warnings that will appear and are preventing you from deleting the Process.

Other warnings could be that you have custom layout, column in different process view, or widget that is used by the process you are wanting to remove. 

If there are no red warnings present, you will be giving one last warning to confirm that you want to delete this Process. Click I confirm and the Process will be permanently deleted.