how to remove lower unit

[buba]

Hi
I use a Yamaha 15HP four stroke, year 2004 outboard, namely the F15AMHS model, on which I must change the water pump impeller, located inside the Lower Unit.
I have read all the Service Manual about the complete procedure on how to do everything except on how to separate the Lower Unit from the rest of the stuff.
Hints will be very welcome.
Thanks

[boats.net]

Remove bolts holding lower unit to mid section and unscrew shift shaft union nut(Shift shaft nut should be in your service manual), then lower unit slides out of housing.