Hi, I need help... :D

Hi im ShifT and im new on PlanetMinecraft
aaaaaaaaaaaaand i need help.
hope youre going to help me....

soo...
I wanna know how can i change my minecraft skin on cracked MC
i tried to change my minecraft skin but it got problems:
everyone else should have steve skin but they have my skin
(my minecraft think that this skin is steve skin... I thinks so....)
and if I ask "do I have skin?" they'll answer :"nope. you dont have skin."
WHY?!
How can i change my skin?
I dont have premium minecraft account and I tried mineshafter and it doesnt work
What to do?!