Turn on your PlayStation, and launch the PlayStation Network. Then select Forgot your password?.
Enter the email address used to create your PSN account. A recovery link will be sent via email with instructions on how to reset your password.
Alternatively, you can reset your PlayStation Network password via web browser. To do this, simply connect to the PSN network and click Trouble signing in?:
Select I forgot my password, and follow the onscreen procedure to reset it: