Once within the settings, scroll down and click the red 'Delete Pipe'-button. As soon as you click 'Delete Pipe' you will be asked to type 'confirm' to prevent you from deleting it by accident.
Think carefully before deleting, once it’s done, all of your Pipe’s information will be gone forever!
Pipefy Tip: You can also delete your Pipe without opening it. Go to your Team dashboard, locate the Pipe you want to delete and click the three little dots on the lower right corner of the Pipe. Again, you will be asked to type the name of the Pipe as an extra assurance you don't delete it by accident.