First, shut down your laptop and remove the charging cable from it. Then find where the battery is stored, (usually on the side or bottom) and take off the plate covering it. Carefully remove the battery, taking note of how the battery is in the slot. Get out your new battery and slowly put it in the same orientation the other battery was and slide it into the battery slot. Screw back on the plates and you have now installed a new battery in your laptop!
If you need to purchase laptop batteries, buy them at Amazon: Replacement HP Compaq 484170-001 Laptop Battery