Generally when you buy an iPhone -- whether a new or a used iPhone -- you will use the Apple ID or write it down your Apple ID data by default. And if the used iPhone you just bought has its Apple ID attached, then you need to replace it with your own.
So never experience of a bad situation like unable to download / install or update an app / a game on iPhone in App Store because of problem on Apple ID.
And if you don't have an Apple ID, then you can make one for free directly from your iPhone, just follow the instructions from the following page.
- How to create Apple ID for free directly from iPhone without iTunes.
- Fix Apple ID Error While Opening App.
And in some circumstance I need to replace the existing Apple ID with another, and here are the steps to do so. You are invited to follow each step if you want to change your Apple ID to another Apple ID without computer or iTunes.
How to change Apple ID to another Apple ID on iPhone
- Enter to Settings, then scroll down till your find iTunes & App Stores.
- On the Apple ID settings, click on the existing email address.
- A box will pop out, just select Sign Out option.
- And now enter the new Apple ID with the password to replace the existing Apple ID then hit the Sign In. If you wish to create a new ID, just select the Create New Apple ID in the bottom part of the interface. See the image below guys.