To delete an active flow version, first deactivate it. If a flow has any paused or waiting interviews, it can’t be deleted until those interviews are finished or deleted. Flows that have never been activated can be deleted immediately.
Available in: both Salesforce Classic and Lightning Experience
Available in: Enterprise, Performance, Unlimited, and Developer Editions
User Permissions Needed
To delete a flow:
“Manage Force.com Flow”
From Setup, enter Flows in the Quick Find box, then select Flows.
Click the name of the flow.
To delete the flow completely, including all versions, click the Delete button.
To delete an individual version, click the Del link for that version.