How do you change a speed sensor on a Volvo 60 series semi truck?

Volvo never used "60 Series" as a truck nomenclature - 60 Series probably refers to the motor - the Detroit Diesel 60 Series - which means that your truck could be from the model years 1986 to 2002 (after ACERT went into effect, Detroit Diesel motors became proprietary to Daimler A.G. products - Freightliner, Western Star, Sterling, and Mercedes-Benz - the only way to get one in a post-02 Volvo would be if it were purchased as a glider kit, and had a DD60 installed).

How you go about doing this depends on the model year. If the truck is old enough, it'll be done by working switches on the back of the speedometer. If it's a more recent truck, you need to have a Detroit Diesel technician hook the computer to the truck and adjust it via the ECM controls.