Use another AppleID in iOS 7.1.2 AppStore? I use iOS 7.1.2 on my iPhone 4 and I would like to change my AppleID for the AppStore. In "Preferences > iTunes &amp; AppStore", I already logged in with my new AppleID, and when relaunching Preferences, I am still logged in with my new AppleID.

But when trying to update an App from AppStore, I am supposed to type in the password for the old AppleID.
I cannot find anything in AppStore to change the AppleID directly.

Is there anything I forgot to do?
You need to update the app using the Apple ID it was installed with. 

For example, say if I install app A with Apple ID B, then sign out and in using Apple ID C, to update app A I need to use Apple ID B.

The most optimal solution to this is re-installing the app on the new Apple ID after saving snaps backing up any data.

From the comments:


  Note that this may require paying for apps and in-app purchases again. You can avoid this in some (but not all) cases by setting up family sharing between the two Apple IDs.