How to remove positive cable from fuse box

I’m replacing One of the main wire harnesses (the one that passes the firewall) but I can’t remove the fuse box from the engine compartment because I can’t figure out how to disconnect the positive battery cable, and the accompanying plugs, from the box. How do I pop the cover that goes over the battery cable and wires to the 3 plugs that plug into the fuse box nearest the front of the car?