You can only delete task lists created by the user himself. If you delete the task list, all tasks in the list will be permanently deleted for all users.
To delete the task list, do the following:
1.Move the cursor over the list to be deleted and click the displayed More list actions button.
2.In the menu that opens, select the Delete 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.