1. From the management settings for the object whose field history you want to stop tracking, go to Fields.
2. Click Set History Tracking.
3. Deselect Enable History for the object you are working with—for example, Enable Account History, EnableContact History, Enable Lead History, or EnableOpportunity History.The History related list is automatically removed from the associated object’s pagelayouts.If you disable field history tracking on a standard object, you can still report onits history data up to the date and time that you disabled tracking. If you disable fieldhistory tracking on a custom object, you cannot report on its field history.
4. Save your changes.