Turn OFF the breaker or pull the fuse to the furnace. That will kill all power. Shut OFF the fuel valve at the tank, disconnect the line on the demand side of that valve at the tank and let that fuel drain into a 5 gallon bucket. Shouldn't be too much, it's only fuel in the line to the furnace. Leaving that line in the bucket go inside and disconnect the fuel supply line to the burner/furnace. This will vent that line and any remaining fuel should drain out into the bucket. At this point it's just a matter of removing any visible screws that appear to be holding the furnace in place. Push and pull on the furnace, if loose, remove it. If it feels like it's still hanging up look for a screw or nail you may have missed. They really don't anchor them into place that well from the factory. As for the old fuel line push it through the floor enough for the unit to clear it as you pull it out. Roll it out of the house with a 2 wheeled cart or get a buddy and carry it out. Done!