Install FTPD on your 3DS
Launch FTPD from the HOME Menu
Note the FTP address shown on the screen
Keep the 3DS and your PC on the same Wi-Fi network
Open an FTP client on your PC or phone
Enter the FTP address from FTPD
Use port 5000 if required
Connect without a username or password unless configured otherwise
Browse the 3DS files through the FTP client
Transfer files by dragging and dropping
Wait for transfers to finish before closing the app
Press the HOME button or exit FTPD when done
Uninstall FTPD if you no longer need it