Read the manual...
But, on the Stbd side of the engine there are 2-3 little plastic tubes that hang down. Place a cup/bottle under them, open the cap to the reservoir and the radiator hose (on my H285, they're in the lazarette)and then turn the little faucets at the top of the little plastic tubes. This will drain the antifreeze out of the engine. Refill with yor favorite fresh antifreeze. Takes about 1 hour. Hope this helps.