Ensure you have the base version of the game installed. Updates cannot run as standalone files.
Use tools like Tinfoil, DBI, or Awoo Installer to side-load the NSP from your PC or via USB/SD card. Update 3.0.3 -v1245184-NSP - megaup
MegaUP has become a preferred destination for the update due to its user-friendly approach to file sharing: Ensure you have the base version of the game installed