You can only delete task lists created by the user himself. If you deletethe task list, all tasks in the list will be permanently deleted for all users.
To deletethe task list, do the following:
1.Move the cursor over the list to be deleted and click the displayed button.
2.In the menu that opens, select the command.
3.Confirm/reject the deletion in the dialog box that opens.
The task list deletion operation is also available in the list settings change window.