There is a drain at the passenger side lower edge of the radiator and one on the passenger side rear of the block behind the exhaust manifold.

Drain the coolant, dispose of it responsibly, fill it with water and run it a little, then drain the water. If you suspect a gunky system get some radiator flush at the parts store and follow the instructions. Then fill it up with coolant.

There have been some heated controversies here about what anti freeze to use. The most important thing is to change it regularly whatever you choose.

Good luck,