i changed my email associated with my apple id, but it did not change on my ipone and i cannot download apps to my iphone. How do I change the email / apple id on my ipone?

Go to Settings>Store>tap the Apple ID, sign out, sign back in.

You're welcome.

Aren't the apps tied to whatever ID downloaded them? Will he still be able to download updates to his apps using his new ID if downloaded with old ID?

For existing purchases he will still have to validate the ID he used to purchase them with the appropriate password, even if the email address is no longer valid. Changing the Store ID setting is necessary to purchased new apps.

Thank you, this was very helpful.

i've got this problem also but cannot delete the account because I have 'find my phone' on which cannot be turned off without a functioning password... any ideas?

Use this article: iOS 7: If you're asked for the password to your previous ...