The account ID that was synced to the device is displayed at the bottom of each page, so you'll always know what account you are using on the device. Simply open iTunes or the App Store on your iOS device and scroll to the bottom of any page to see which account is currently in use. You can also see this in Settings under the Store option.
Changing your account:
From Settings, choose Store. You can then sign out and create a new account
Settings >Store>tap on your AppleID. Log out and log in with your new account info