Yeah, water changes work wonders to dissolve bad stuff like Ammonia. If you change 50%, your 4ppm is down to 2ppm, another 50% WC and you're down to 1ppm, another to 1/2ppm, 1/4ppm etc. Don't do all these WC in one day you know, but over the course of the next couple of days. Generally if your tap is the same as your tank water except for the ammonia, then the fish will appreciate the water change. Look on the AmmoLock container for direction. I seem to remember you could only add it 3 times before they suggested doing a wc. Personally, I would do a water change, then add the ammolock. Buy doing this, you are first removing half of the ammonia present by taking it out and replacing it with fresh tap water, secondly, you are trying to "lock" the remaining ammonia in the tank witht he ammolock.