2004-2009 Honda TRX450R/TRX450ER Service Manual, Page 171Get this manual
COOLING SYSTEM REPLACEMENTAIR BLEEDING NOTE When filling the system or reserve tank with coolant, place the vehicle on flat, level surfaceRemove the right front fender ('04'05: page 3-6, After '05: page 3-6)Remove the radiator cap
Remove the drain bolt and sealing washer, and drain the coolant from the systemReinstall the drain bolt with new sealing washer and tighten it securely