Under the plastic cap on the top. Then you need a 1 1/16 socket and probably a breaker bar as the rod is usually in pretty good.
You remove the old one with a socket and breaker bar after using penetrating oil and time (Overnight), to help loosen the nut. Then install a new one with the same socket and breaker bar after putting Teflon tape on the threads. Do NOT overtighten!
You will need a 1 1/16" socket like the others have said and to get the old one out, i used a standard breaker bar. All you need is enough leverage, do not go crazy. If you do not have a breaker bar, use a long piece of pipe over the socket wrench handle and just lean into it a bit. Do not forget to dope up the threads putting it back in. If you have obstacles on top, maneuver it into the hole first and then dope it up before you drop it in place. The head of the rod may hot something else up top. Mine was a bit tricky to maneuver between other pipes, the exhaust for the water heater and rafters.
No, Try an active anode. One which must be plugged in to generate a charge in the tank that "May" solve this problem. And will also help with corrosion much more than a standard type anode rod. BUT, it depends upon the root cause of the problem.
It needs to be replaced between 12 and 18 month depending on the water in your area.
Just cut it with a hacksaw. No it should not touch the bottom of the tank because you will not know when you have snugged it down.
See instructions at the link below on how to do it. http://www.rheem.com/docs/FetchDocument.aspx?ID=aedbbc95-9a6b-4780-aa23-b0ed9abe41cd
Maybe but that smell is sulpher in the water
Gets rid of rotten egg smell from water heater. Had to use electric impact to get the old one loose to get out. Works fine.
You should get a segmented rod which has a flexible cable running down the inside which allows it to be bent at the joints where there is insufficient overhead clearance.