Dell Vostro 14–3478 Owner's Manual page 16

b Remove the 3 (M2x5) screws that secure the base cover [2].
4 Flip the computer and remove the screws (8 screws - M2.5x8; 3 screws - M2x2; 2 screws- M2x5) that secure the base cover to the
computer.
16 Removing and installing components