If you are wanting to replace the magnezium anode rod you need to shut off the water to your heater and open a valve on the hot side to relieve pressure. The rod or whats left of it is removed from the top of the heater. I'm not sure but I think it's 1 1/8 inch hex nut. You can use a socket or pipe wrench to remove it. Turn it counterclockwise to remove.
You can replace it with standard magnezium rod to extend tank life or if you are haveing odor problems especeilly on the hot side you can get a aluminum rod to help with that. Generally if you are getting sulphur in your water it will smell like rotten eggs. Before you install new rod you should wrap the threads several times. Tighten it up good, close the valve you opened and turn water back on to heater. Check for leaks and bleed air out of hot water lines. Hope this helps you. Thanks