Before beginning, remove any DNSs (like Tubehax) that you may have on your 3DS. This can interfere with the downgrading process.
- Grab the sysUpdater app from here and place it into the '3ds' folder of your SD card.
- Make a folder called 'updates' on the root of your SD card.
- Place all of the CIAs for the update you wish to downgrade to into the folder. (I cannot link these for legal purposes. Sorry!)
- Eject your SD card, put it into your 3DS, and boot.
- Open up the Homebrew Launcher in your entrypoint of choice and start the sysUpdater app.
- If everything goes well, you should have some options. Since we're downgrading, you can go ahead and press the Y button.
- Wait and DO NOT touch anything. The app will tell you when it is done. (It took me less than 5 minutes)
- Once the app prompts you that it is done, wait. It will reboot automatically.
- Bite your fingernails in suspense. If everything goes correct...
- Your 3DS will be downgraded!