Change length of several lines simultaneously.

[Pooya <Input Pooya de>]

Hi,

this is a very simple question for a very simple task. But I wonder, why I am not able to do this.
Is there any trick?

I am trying to change the length of several lines/arrows simultaneously. I selected them all and tried with 
the "object-change-tool" to drag a line´s end.
Nothing happens.

What do I miss?
Thanks!