How do you drain antifreeze and refill in 1994 chev caprice?

First, make sure the cooling system has cooled down. Then open radiator cap and place a drain pan under radiator drain (usually on the drivers side lower corner of radiator facing the engine). Open drain and wait until system drains completely, the dispose of used coolant as per local regulations. Then it is a good idea to flush the cooling system with clean water before filling. Do this by means of a flush tee (if you can) but if not, just take a hose and run water into radiator cap opening while engine is running (be careful to stay clear of all moving parts ie: fan, belts, alternator, etc.) and have heater set to hot and fan on so heater core gets plenty of flow. After water runs clear, you can shut engine and water off and again, wait for the system to drain completely then close radiator drain valve (petcock). There will be some residual water in system, so you can mix the new coolant a little bit stronger than 50/50 but depending on the size of engine (4, 6, 8, or 10 cylinders) it will vary some. As a rule of thumb, in a V8 I use 1/2 gal straight coolant then top off with 50/50 mix.

I also recommend checking the radiator cap for proper release operation and replace if it does not test good.