Your CRM tracks all changes made to the Lead fields. Information on these changes can be viewed in the Field History report for each Lead individually. 

In order to view the Field History report click on the Last Saved link in the Current Lead Status widget:

The Field History report will pop up as shown in the below example screenshot. The report shows a list of the fields that have been modified including the old and new field values, the time when the fields were modified, the source of the new value, and the user who made the modification:

You may sort the report in ascending or descending order by clicking on any of the column header names, or perform a search using the Search box:

Finally, you may also export your report to a CSV or an Excel file using the Export button: