Instructions
Boot up your PlayStation 3 and log in normally to the account you wish to delete by selecting it from the main menu.
Scroll to the left side of the cross media bar (where all users are displayed) and highlight the active account. It will have a little white dot next to it.
Press the triangle button on your PlayStation 3 controller to bring up a sub-menu. This menu will appear on the right side of your screen.
Select the "delete" option from the menu. A pop-up screen will ask whether you are sure you want to delete the account. Simply confirm and your account, along with all your save files and account information, will be gone forever.