Originally posted by another user
Changing your password on PS3
1. On your PS3, navigate to the PlayStation®Network icon on the XMB and choose "Sign-in".
2. You will be asked to enter your current sign-in ID (email address) and password. Note if you have enabled the auto sign-in option you will not need to enter your current sign-in details.
3. If the console you are attempting to sign-in on is activated against your account (that is, you have downloaded content, either free or paid-for, using your account on the console), you will be prompted to enter a new password. Once you have updated your password, you will be logged into PlayStation®Network as normal and will be able to use all available online services.
4. If the console you are attempting to sign-in on is not activated against your account (that is, you have never downloaded any content using your account on the console), an email will be sent to the registered sign-in ID (email address) associated with your account. This e-mail will contain a link that will enable you to change your password. Open this email, click on the link and follow the instructions to change your password. Once you have changed your password you can sign-in to your account using your new password.