Remove the Fan shroud and Clutch fan.
Remove all the belts.
Remove the Radiator for more space to work.
Remove the bolts that hold in the water pump.
Clean the gasket mounting surface.
Apply RTV of your choice.
Torque water pump bolts to spec.
Reinstall Belts, Radiator, Fan and Shroud
Fill with Coolant/Water Mix of your choice.
Start and Drive
Remember to let the RTV time to cure.
----------OR-------
Pay a shop.