how do i remove the battery from my peugeot boxer?

i need to remove the battery on my peugeot boxer and the handbook is not at all helpful. I have opened up the cover to the battery compartment and can see that one of the terminals looks easy to release but the other one has a what i can best describe as a plastic box with wires in over the top of the terminal i need to release. I cannot see how to take this plastic tray off in order to realease the battery and take the battery out.