how to change current city

I would go into Menu, Setting, About Phone, System Updates, and update the Data Profile and PRL. 


A better question to ask you would be..is the phone showing the wrong time in the notification bar or is the wrong time showing on a app. If it's an app, you might just have to find another app because sometimes that happens. If it's the time in the notification bar, that's from the network, and doing the updates shown above "should" fix it. Otherwise, call Sprint, they may have to fix it from their computers.