How to change screen name in ym?

my screen name for example is ';simplicity service';

i want to change ';simplicity service'; to ';s service';

so i change my contact details, simplicity service to ';s service';



when i ask my friends if my screen name change

they told me that it dont change to ';s service';



what will i do so that my screen name will change in there screen?How to change screen name in ym?
click on my account next to sign out and youll find all the options there