Nintendo DSi Firmware 1.4.2 , you generally do not "download" a file from a website to install via SD card. Instead, Nintendo DSi systems use an over-the-air update system directly through the console's settings. Official Way to Update Your DSi
Note: As of today, the final official firmware for the DSi is version 1.4.5. If you perform an official update now, your console will likely skip 1.4.2 and go directly to 1.4.5. Impact on Homebrew and Flashcards Nintendo Dsi Firmware 1.4.2 Download
Some users mistakenly think updating to 1.4.2 will revive the DSi Shop. It will not. The Nintendo DSi Shop was permanently closed in March 2017. No firmware update can bring it back. Nintendo DSi Firmware 1
If your DSi is already on 1.4.5 and you want to go back to 1.4.2, there is no official "downgrade" tool from Nintendo. This usually requires Custom Firmware (CFW) Twilight Menu++ If you perform an official update now, your
Modern DSi modding has evolved. With tools like TWiLight Menu++ and Unlaunch , you can run backups and homebrew on the latest firmware (1.4.5) without breaking a sweat.
Unless you are a homebrew developer testing legacy code or a completionist trying to un-brick a specific flashcart,