I was told that my upper unit water pump is not pumping.Is this easy to change and how?

I am a first time boat owner of a 1979 100hp evinrude. I have no water coming out of spout by the engine. I was told the upper unit water pump by somebody. Is this hard to change or should I not be cheap and take it in. Mechanics want 177.00 and the water pump kit is only 30.00.