To delete a lead, navigate to a lead's page and click the symbol in the top right corner of the page.
We don't recommend you delete a lead unless absolutely necessary. Even invalid leads are important for reporting purposes. If a lead is in any other stage ("Prospect", "Lead", "Client" or "Lost"), you should still consider it a good lead, even if it was lost at some point. Deleting it would get rid of valuable data.
Note that Invalid leads are not included on the majority of LeadSimple's reporting, except where applicable, such as in the marketing performance report.