Downloading firmware from unofficial sources carries risks of malware or corrupted files. Only use files verified by multiple trusted community members.
Log into your account at owners.nissanusa.com (or your local Nissan site). Occasionally, Nissan will post here, especially for models like the Nissan Rogue or Altima with the NissanConnect system. nissan firmware download
If the "firmware" update you are looking for relates to critical vehicle components (like the Engine Control Unit or Transmission Control Module), these are generally not available for public download. Nissan will post here