I havent changed mine, I just rinse it in the used tank water when I feel it needs to be done. Im sure that whatever good was in it, is gone, but I find it just an additional place for good beneficial bacteria to grow, so that is why I leave it in.
In my opinion, any excess ammonia in the tank should be taken out with a water change asap and not left in for the ammonia remover to do the job.
Guess they were good for a new tank set up, but since the tanks are cycled, its really not necessary IMO.

~ kate