Why do you need to replace it? Is it discolored or disfunctional?
Before you replace it, are you sure it is bad? If it's not reading, the problem "May" be in the Wiring or the Sending-Unit in the Gas-Tank.
Sometimes it's a loose or corroded wire/connection or a bad ground-strap to the outer sending-unit. Other times the Float in the tank has developed a leak (Brass Float) or the Resister-Strip that the Float-Arm bears against has burned out.
You can check connections and the continuity of the wire to the tank, and check the guage by Grounding-Out the wire that leads to the tank.
You can test the Sending Unit by removing it from the Gas-Tank (probably need to Drain/Drop tank to get at it) and can test the Unit with a Volt/Ohm Meter/Tester.