how do you replace the head gasket on a 1999 chevy blazer?

Answer 1

That's not a simple answer.
Go buy the book for $22.00.
Haynes, or Chiltons.

Answer 2

Remove everything attached to the head. Remove the head, replace the gasket and reattach everything that you removed. Wala....simple as that...Of course, this is a "smart ***" answer, but if you're having to asking how to do it, you have little chance of completing it successfully. It is a very complicated job for a novice. If you are going to try it anyway, find a good repair manual and follow it step by step.