Replacing waterpump

I own a 95 aurora and I'm replacing the waterpump (gonna try myself) and was wondering if I need to remove the thermostat, and drain the coolant? I have changed alternators and starters on my other vehicles, but only taught myself over the years, but have never changed a waterpump. Any advice would be greatly appreciated. And should I switch to the dex-cool or stick with the green stuff?