I replaced mine a couple of years ago without any idea how to do it(below are links on step by step instructions). It took me about 2 hours & was easy. When they say water pump, really all you are replacing is the impeller (& replace the seals if needed). The impeller on the left is bad. The one on the right is how it should look.
I will replace mine at the end of the summer. It is good to replace it every few years or so. I figured since we talk about repairing our trucks. We needed this write up for our boats also. You can save hundreds of $$$ doing it yourself. I think it cost me about $20-$30 for an impeller last time.
Evinrude & Johnson: