You need to remove the battery [remove the negative (-) side first then the positive(+) battery connections] and lift the battery out. You need to disconnect the small fuse box first IIRC from it's fixing, it unclips using a small flat blade screwdriver at the the back of it to release the clip. Once released you can then hold it up out of the way so the battery clears it when you lift it out.
Once the battery is out you can see the 4 holes in the existing plastics where the 4 pins on your cover fit to hold it in place,