To delete a Marketing Source, from the main menu, arrive at the Marketing Sources setup with this path: Setup > Proposals > Marketing Sources.
The Marketing Sources list will be displayed. Locate the record you want to delete, and then click on the Delete button.
A confirmation message will be displayed. If the Marketing Source has never been used on a Proposal, the record will be deleted. If the Marketing Source has been used on a Proposal, the record will be marked as inactive. Click on the Yes button to confirm the deletion/inactivation of the record.