You should ask your lawyer to make a hardship showing and see if the date can be moved. Depending on the judge it can be difficult but we have been successful in the past. Often it depends on the reason for the need to chage dates.
As we don't know enough about your case, you should not consider my answer to be legal advice. You would need to consult with an attorney at length and include details about what has occurred in order to adequately assess your criminal exposure.
What I usually do in these situations is have my client complete an affidavit authorizing me to appear on their behalf. Depending on the charge and the court, judges in NYC will sometimes even let an attorney resolve a minor criminal case without the client being there.
Should you wish to discuss this matter further, please feel free to contact me at anytime.
You will need to contact the court directly. Usually the court will grant a postponement for good cause. If you can not appear, an attorney may be able to handle the case without the need for your appearance provided you give him the appropriate authorization.