I run the regular green coolant/antifreeze in my rigs when I have to do a refill when a radiator or hose goes.
But if you're looking to just to replace the Dexcool with the same as part of routine maintenance, open the draincock on the bottom tank of the radiator and then refill it.
They also sell flush kits at your local AutoZone or Advanced Auto Parts if you want to flush it first.
But typically, unless the old coolant is extremely contaminated, a drain and fill suffices in my experience.
shop.advanceautoparts.com