1. Turn your Sony VGN-FZ420 laptop over.
2. Find the laptop battery release button lock for your Sony VGN-FZ420 laptop.
3. Now that your Sony VGN-FZ420 laptop battery is unlocked, find the battery release button down.
4. Holding the laptop battery release button, gently pull your battery away from the laptop.
5. Now that your Sony VGN-FZ420 battery is removed, grab your replacement Sony VGN-FZ420 battery for installation.
6. Insert the battery into the slot. Push the Sony VGN-FZ420 battery towards the laptop and secure it in place.