I do believe you would have to start a new account if you want a different Id.
I'm pretty sure he's asking how to change his PSN ID (using the GTPlanet iPhone app) from his old one to his new one, that is displayed on forum posts. The one between our location and post count.
As for the answer, I'll try to find out when I go to bed in a few minutes. That's where my phone is.
J0SH1Nahh I go to profile and it just takes me to my page and I can't change it.