Whenever you purchase anything from iTunes or App Store you have to use your apple id to sign in. Moreover, in iClouds and App Store you also have to sign in with your Apple ID.  It is pretty much possible that you may not have access to the email id associated with your Apple ID. Also, if you change your email id regularly, then there might be same reasons for changing your apple account email as well. In that case below is how you can do it.

How to change Email Address Associated with your Apple ID?

1. First open Safari on your iPhone, iPad or Mac.
2. Now Go to http://appleid.apple.com/.
3. Here, log in with your current details.
4. If you are asked to verify your identity do it.
5. Now you will see Edit option under the accounts section.
6. Under Apple ID Tap or click on Change Email Address.
7. Enter your new email address (make sure you have not used it in any of your Apple accounts).
8. Tap on Continue.
9. You will now need to verify your new email ID. Open your email id in a new tab and verify the code sent to you.
10. After verifying the email tap on Done to save your changes.

That’s it! Enjoy your new email address associated with your Apple account.