Darcey, you don't need to remove the rad. Just find the drain down valve.(it will Have a little brass connection point)Connect hose. Make sure the boiler and system is off(IMPORTANT). Turn off the water supply to system. Open the drain down valve and make sure that the hose discharges somewhere that will not be ruined by gallons of black or brown sludgy water. Switch water back on and let the system flush through until the water is running clean. This is now a good time to add a system rust inhibitor. Even easier if your system has a header or expansion tank in the attic. Close the drain down valve again and fill the system. Bleed the rads and switch on the boiler and controls again. Carry on bleeding rads until it is air free. Disconnect hose.