Since this is a somewhat high reading, if your going to keep corals, the best way out is to make some large partial water changes. A 50% water change will reduce nitrates by 50%. Test your newly mixed water first though to make sure that is not a source of nitrates and/or phosphates.
You will need to do 5 or 6 large partial water changes to get the level way down. Do them several days to a week apart. If you think 50% is too large a water change, you can do it by changing 25% or 33% of the water, but you'll need to make more partial water changes.