If your tank was established all ready, you can do a water change. If it was just the sand bed being stirred that caused it, that will help.
If it is the LR, the dieoff will be gradual and you may have a harder time keeping the levels down until it cures.
You will always have a little dieoff when adding LR, just because you are taking it out of the water. That is normal, but .5 ammonia is kind of high.
A water change isn't a bad place to start.