Instructions
Remove the memory card from the memory card slot on your Nintendo DS.
Insert the memory card into your computer's card reader.
Open your web browser by double-clicking on the icon via your desktop.
Go to the "R4 1.19" website (see References link).
Click the "Download R4 1.19" icon at the bottom of the webpage.
Click on the "Start" button, and click on the "Computer" icon.
Click on the "Memory Card" icon. You will see a "_DS_MENU" icon and a "_DS_MSL.NDS" icon. Highlight and delete the files.
Click on the R4 1.19 software icon, and drag it into the "Memory Card" window to install the firmware to the card.
Remove the card from your computer, and put it back into your DS. As the Nintendo DS boots, it will boot from the firmware on the memory card.