If it's just the motor, usually its 2-4 bolts to remove it from the resevoir and most times the engine has to be pulled while trimmed all the way up after opening the manual release to get at the back bolts. I've never personally done one on a Johnson/Evinrude but I recall the other mechanic at our yard doing one and the motor was off the transom. I recently did a Merc and it also had to be pulled.
Just remove the mounting bolts, disconnect the wiring harness while taking note the way it was routed into the cowling, and pull it off. Put the new one on, I'm sure there is a gasket or o-ring of some kind. Fill the resevoir while the motor is all the way up and you should be good.
