Instructions
Press the "Power" button. Eject any discs in your PS3 by pressing the "Eject" button.
Navigate to the "Settings" icon. From the sub-menu, open the "System Settings" folder.
Click on the "Restore PS3 System" option. A disclaimer message will appear. The message will describe that the original firmware version that was installed in your console will be restored to factory firmware. Any other trophies, profile information and saved games also will be permanently deleted.
Click "Yes" to continue the restore. You can follow the progression on the progress bar. Once the system has finished rebooting, the console will automatically reboot. You will have to input all yoru settings and profile information again.