To enable/disable an activity set:
In the Action Bar, click the icon, and under Modules, select Activity Sets.
Under the Action column, click to edit the name of the activity set.
The Activity Set Name field becomes editable.
Under the Enable column, select the check box and click the Save button.
The Activity Set is enabled or disabled as per your selection.
Note: The activity sets that are used in a sales opportunity cannot be disabled or deleted.