The Task History on the task details page tracks the changes to the task. Any time a user modifies any of the fields, a new entry is added to the Task History. All entries include the date, time, nature of the change, and who made the change.
Select Home > Tasks > My Tasks.
Find the task you want to view the history for in the task pane.
Click on the View History icon to the right of the task for the history to be displayed.