The memory is easily accessed thru a door on the bottom of your laptop. Just turn it upside down, remove the 2 screws from the access door in the rear next to the centronics connector. Remove the access door and you're able to access the memory slots.
Click the Crucial link on this page and enter your manufacturer (Dell), product line (inspiron), and model (5000 series). The Crucial site will show you the correct memory modules to purchase.
Mike