How were you notified of this change? Was it via an email? If it was you are being scammed. I get these phishing emails in my Apple mail every few days. They all tell me I need to change my password, my account has been frozen or will be deactivated if I don't take immediate action. If you can still access iTunes, your iCloud, email, etc then you're being scammed. Don't fall for it. I haven't been forced by Apple to change my password ever.