no heat but i have defrost ne answers

i ran in to a problem this winter and it is no heat in my car, the defroster works and the blower motor works realy good at blowing out cold air instead of heat..... im asuming its the thermostat....... if so how do i go about draining the radiator with out taking the front bumper off, or do i even need to take the bumper off ??? i have a haynes that shows how to do the rest, cept for draining the radiator......