How to change apple ID for a local app store on iPhone4s?

I have iPhone 4s, recently notice an update of OS 6. After this recent update of the iOS 6.0,
I was about to update some applications such as viber and whatspp etc,. I saw a message saying that my account is not valid for use in the US store, and I must switch to the local store,
I have another apple ID, i coundnt find the way how to switch it? I used to switch several times, but after this update it looks nabt features are completely changed,

any advises will be appreciated, with thanks

To change apple id phone4s: tap Settings >> General >> Reset >> Reset All Settings. Once the iPhone reboots, go into the app store and attempt to download an app. You will be prompted to enter in a user name and password.