Disconnect power to the hot tub at the main breaker or fuse panel.
Locate the junction box near the hot tub that provides power to the light. Remove the retaining screws and pull the cover off of the box.
Remove the retaining screw that holds the retaining ring to the front of the light fixture in the hot tub. Pull the retaining ring off of the fixture and lift the fixture up and out of the mounting area. Pull enough wire out of the mounting space to access a dry work surface on the edge of the hot tub.
Cut the wires where they enter the old fixture then set the fixture aside. Strip several inches of insulation off the ends of the wires. Also strip several inches of insulation from the ends of the wires on the new fixture at the end opposite the fixture.
Dry the wires thoroughly. Twist the bare ends of the old wires around the bare ends of the new wires. Wrap the union in several layers of electrical tape, extending the tape several inches up the insulation on both sides.
Have an assistant pull the old wires at the junction box while you feed the new wires into the conduit in the fixture. Continue feeding the wires into the conduit until the new fixture fits into the mounting space.
Set the fixture into the mounting area, insert the retaining screw into the retaining ring and tighten it securely.
Cut the wire to length at the junction box, leaving 3 inches of slack at the box. Strip the insulation from the wires and connect them to the wires in the junction box according to the manufacturer's instructions.