To turn on audit tracking in CRM:
Go to Advanced Settings > Auditing


Select Global Audit Settings

Ensure Start Auditing is checked off and hit Save.

To begin viewing the Audit History:
Select Audit Summary View:

On the summary view, enable the filter.

Under Entity select Custom Filter to sort the logs by entity type.

In the drop down select Equals > [Select preferred entity for audit history]
Then apply additional filters as needed to narrow down the search:

Select a record by clicking on the white space. A page will pop up identifying the field(s) which was updated.