1. Turn your Toshiba A300D-21C laptop over.
2. Find the laptop battery release button lock for your Toshiba A300D-21C laptop.
3. Now that your Toshiba A300D-21C 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 Toshiba A300D-21C battery is removed, grab your replacement Toshiba A300D-21C battery for installation.
6. Insert the battery into the slot. Push the Toshiba A300D-21C battery towards the laptop and secure it in place.