If you’re wondering how to change your apple ID on your iphone without doing a full settings reset, follow these steps:
1. start iTunes
2. Sign out of your account in iTunes.
3. plug your iPhone in and let it finish the sync process.
4. open the app Store app on your iphone and choose any free app (or an app you’ve already purchased) to download.
5. you’ll be prompted to enter your new apple ID/password.
Hope that helps anyone out there that’s been having issues with this or wondering how to do it.