According to the same-day change policy of JetBlue, you can alter your flight ticket on the same day for Blue, Blue Plus, or Mint fares for a flat cost of USD 75 without incurring any fare difference. Although, JetBlue change flight policy to same-day is free for mosaic members and blue extra fares. 

To amend the JetBlue flight on the same day, you must go to the Airline kiosk before the flight's scheduled departure. Over the counter, you can connect with the executives for making changes and get answers to your questions. In case the Airline staff is unable to connect with you, dial this number +1-800-865-1848 for prompt assistance.