The Auto-Update option in the Activities List provides a way for you to update or delete activities en masse.
Go to the Activity List tab and select the activities you want to update. You can filter these using the Show drop-down list to select a date range and the User drop-down to select one or multiple users, or by right-clicking in the open area and choosing Options>Date Range or Options>User.
You can further filter your activities by right-clicking and choosing Options>Activities to select the types of activities you want to view. Right-click in the open area below the activities list and select Options>Auto-Update. From here you can choose to complete or delete the activities you have selected.