Instructions
Through Your Computer
Log in to the PlayStation Network website with your current registered email address and password.
Click "Change Sign-In ID (Email Address)" under "Account Management."
Enter your new email address in the box, then click "Continue." You'll be taken to a new page saying that the update was successful. Click "Continue."
Click "Change Password" under "Account Management."
Enter and then re-enter your new password. Click "Continue," then "Continue" again to return to the "Account Management" page.
Through Your PlayStation 3
Scroll to the "PlayStation Network" tab of your PlayStation 3's "XrossMediaBar" -- or "XMB."
Log in with your current email address and password.
Press "X" to select "Account Management," then "Account Information."
Select "Sign-In ID (Email Address)," then enter your current password and click "Continue." You can now change the email address with which you sign into the PlayStation Network. Select "Confirm" when done.
Select "Password" from the "Account Management" menu, then enter your current password. Enter your new password twice. Select "Confirm" when done.