The new generation vehicles will have many sophisticated systems such as drive-by-wire, navigation, traffic congestion control, road guidance, and advance crash warning. Already, dozens of onboard computers control complex vehicle functions. From time to time, an onboard computer needs reprogramming. Currently, dealers manually reprogram software in onboard computers via a wire based electrical connection. Updating software wirelessly is a preferred alternative to the manual method because the vehicle need not be physically present at a repair facility to perform the update. Wireless software reprogramming will save customers' and technicians' time and money. In this paper, we present a wireless download algorithm for reprogramming of vehicles' electronic control units, using current wireless technologies. Our algorithm proposes a hybrid infrastructure that combines wireless unicasting and multicasting data delivery.