Well first we need to know what year it is....
Is it an automatic bilge pump or does it have a float?
Make sure it is the bilge pump and not the float or evena fuse.
To get the pump out, usually it twists off or pulls off. I would need a pic to see what pump it is. Pull the old one out, diconnect the hose, make sure its clear, then clamp it on to the new pump, splice the new pump's wires to the boat's electrical, and away you go.