High Ammonia
We need more information on your tank.
Number of fish? size? Filtration System? Age of tank water?
But to get your ammonia levels normal I would recommend 20% water change daily, use your test kit and start to change the water twice a week (depends on what you test kits tell you). But remember, after the ammonia comes the Nitrites, so expect more troubles. Continue doing 20% water changes at least twice a week. After you finish with your New Tank Syndrome you will be able to increase to twice a month.
As far as pH and water hardness, I wouldn't mess with this unless they values are very high, if you have a 8.5pH I would not try to move it unless you are thinking on breeding. ph is very hard to control, pH drastic changes during a week are more dangerous than a stable pH of 8.5. If you are not comfortable, ask Petco to test their own water parameters with you present, you will see no mayor difference with your water.
Good luck..