If you can't remember your Apple ID Password, or want to change it, use the password retrieval process at My Apple ID.
Follow these steps to change your Apple ID Password:
1) Go to My Apple ID and click Reset your password.
2) On the next page, enter your Apple ID Name and click Next.
3) Authenticate by email or by answering the security question.
4) By following the emailed link or answering the security question, you'll be presented the option to reset your Apple ID password.