What is the proper procedure to replace water pump

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When I started my x3 I noticed it wasn't idleing correctly like it was missing. When I started driving I heard the belt start squeaking then power steering went out and started to get warm so I shut it off immediately. Once I popped the hood I noticed the water pump pully was crooked.. could you please explain to me if that is the cause of the other problems and the proper procedure to replace it.. thank you..