The quick and easy solution to pollution is dilution...ie: a number of partial water changes will "dilute" the nitrAtes and lower your total...Temporarily...
The real question is not so much how to lower them, but where are they coming from...
Over feeding, dirty filters and lack of nutrient export or nitrate reducing bacteria are the most common causes, along with using tap water which may contain nitrates...
Can you share a bit about how your tank is set up...Filters used, amount of LR/LS, sump/fuge, skimmer,number of fish/inhabitants, feeding habits/schedule, water change/maintenance schedule, etc...?