Original Source: How To Change Apple ID on iPhone
Having an iPhone or iPod and not having apps like iTunes just don’t go together. You use your Apple ID to access such apps to make full use of your device and why shouldn’t you?
You can browse through a multiple of exciting apps on the App Store: more than 108 of these listed in 14 different categories.
Unfortunately at times you find out that the app you really wanted, whether you are buying it or it’s free, is only available in some other country. What would you do if you really wanted that app? You would create a US iTunes account for US-only apps and this article will teach you how.
You will find it helpful for altering your existing ID or to switch over to some other ID.
Steps for your Device
Firstly, you must authenticate the account that is presently in use by you for accessing the apps. In your iPod or iPhone , go to iTunes or App Store and reach the lower part of the page. In App Store, if the app product page is open then return to the main screen or you can hit the Categories or Top 25. It will show you the three Top categories for apps: Top Paid, Top Free and Top Grossing. Reach down again. You must have had to make an Apple ID if you ever bought an app or got a free app.
At the AppStore or iTunes, you will see your ID at the bottom of the page.
After you have confirmed what ID is in use, go to Home and start Settings .In settings go down and tap on Store.
Out of the two options you see, Apple ID and Sign Out, if you select Apple ID you will see your settings for payment details like billing address, phone number etc. for this account that you are using. It will also show you the country whose iTunes Store you are buying from and you can change the country/region by following the instructions on your screen and agreeing to the terms and conditions. You might have to alter your billing details.
Tap your existing Apple ID and you can change your ID email when it gives you your email, password etc.
If you want to sign in with another Apple Id that you have, just go back and Sign Out. Now you can sign back in with the other ID.
Otherwise, you will be automatically asked to Sign In when you buy apps or iTunes next time after you have signed out.
Steps for iTunes on Desktop
If luckily, you are operating from your desktop or laptop where you have the luxury of a keyboard then you can easily change your Apple ID and associated billing information by opening iTunes and going to Store and click View My Account. It will ask you for your email.
It will ask you for your password for confirmation. Once through, it will give you all your Apple ID details that you can then change.
If you don’t have the access to your computer then you can go to appleid.apple.com to handle or modify your information.
Let me know in the comments if you found this article of any help!
How To Change Apple ID on iPhone