How to change steam heat to hot water system?

if i were you i would look into purchasing a heat exchanger it will look like a torpedo.it will be a shell and have a copper coil in it.the steam will feed into the shell and the hot water will cir.threw the coil.i would not replace the steam boilers.then u can run baseboard .they do sell cast iron baseboard its expensive but holds the heat longer than fin tube.the steam will maintain temp. in the heat exchange and a call for heat will bring on a pump to cir. water threw the baseboard.u can change it to hot water by adding expansion tank and changeing the control setting i have done it.the heat exchanger is the way to go steam is very efficent source of heat.