Frost is removed through the application of (typically) Type I de-ice fluid (information about de-/anti-ice fluids). Fluid application is generally from a truck with a lift so that the operator can spray the aircraft from above. The fluid is generally hot, diluted with water and under pressure so you'll see lots of steam coming off of the fluid spray. The truck will drive around the airplane spraying the wings, tail and fuselage as necessary to completely remove snow, ice and frost.
Some airports have static mounted de-ice towers that are more like cranes and some operators have automated trucks where there is no operator in the lift and they can do the whole operation from the cab of the truck.