I'm no expert on Etecs, but normally the gearcase anode is held in with a screw under a cover on the top of the back of the "lump" above the cav. plate. If it's been serviced recently it should come out with little or no hassle, as that screw is usually one of a few that holds the gearbox onto the bottom of the leg.
One tip - before loosening the screw, mark the case at the fin with a pencil so that the new one goes in at exactly the same angle, otherwise you will be adjusting it for the next 6 outings!
One on the bottom of the clamps is usually two screws vertically up. The fun starts if you shear the heads, so don't be too enthusiastic to start with! Your manual should say what feature on that one will either dissapear or appear from under the zinc as a "change now" indicator.
