1997 BMW 328 How to Change Head Gasket

I need to replace the head gasket and the water pump of my 328! BMW 4 door b/c the car is overheating and the car is exuding white smoke out of the back from water. How do I change the head gasket and where can I buy it? Also the water pump?
DO I need to fix anything else besides changing just the gasket or do I need to do anything with the valves? Thank you!
Tara
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