Instructions
Go to the PlayStation Network icon on the PlayStation main menu and select the sign-in option. If a user is already signed in, press the triangle button while highlighting "Account Management" and select "Sign Out."
Highlight the username field and press X to open up the virtual keyboard. Enter your username, which is the email address associated with the account, using this keyboard. Alternatively, if you have a USB keyboard connected to the console or the keyboard attachment on the controller, you can use either of these to enter your username. Press start when you are finished.
Highlight the password field and use the same process to enter the password you use to sign on to your account. Press start when you are finished. Scroll down to the sign-in button and press X to sign in to your account.