A couple of things that should help...
Warming the hose makes it easier to remove from fittings.On most boats on which hoses pass through inaccessible areas, connecting the new hose to the old and pulling it through as you pull the old hose out can make the job a lot easier.Use a male-male connector...cut the edges of the old AND the new hose as cleanly as possible, 'cuz you want to be able to butt 'em together tightly to make the smootheest unbroken connection possible. So you want to use PVC cement to keep both pieces on the connector...'cuz hose clamps can get caught and duct tape isn't likely to hold.Vented loops and y-valves--which may or may not be needed and/or may be in the wrong place-= can add a new challenge, but if you have just a LITTLE more mechanical ability than is needed to turn a doorknob, you should be able to figure out to deal with those.