1968 Model Mercury 6 Horse Outboard Boat Engine?

I recently aquired an old jon boat and engine. How do I drop the lower unit on a Mercury 6 horse to change the water pump impeller?1968 Model Mercury 6 Horse Outboard Boat Engine?there will be several nuts a few inches about the prop the case will split there allowing you to access the impellor housing. however be carefull not to pull the water tube loose from the head or you'll be taking it apart at the upper end of the lower unit to get the tube back into place