EDIT: This tutorial maybe outdated, technically it still work but please use Plailect's Guide, it covers even more things:



https://plailect.github.io/Guide/



EDIT: MANY USERS ALREADY BRICKED THEIR DEVICE, SO BE ABSOLUTELY SURE WHAT TO DO, THIS IS VERY DANGEROUS. WITHOUT A HARDMOD AND A NAND BACKUP A BRICK IS PERMANENT!!!

I'm doing this tutorial quickly only because we don't want to answer all "How to downgrade" question-threads seperately.

All credits belongs to TuxSH, Jason Dellaluce, Steveice10 (and some other, don't know who else right know)

KEEP IN MIND: BRICKS CAN HAPPEN AND HAPPENED TO SOME USERS!!! NO WARRANTY FOR A SUCCESSFUL DOWNGRADE!

1. You need a 3DS with any hax installed, if you have non, use Browserhax (http://yls8.mtheall.com/3dsbrowserhax.php) by yellows8 or menuhax. And of course, at least boot.3dsx in SD card root.

2. Download sysupdater and, unzip it and copy it to sd card:/3ds/ (if it does not exist, just create it...)
Mirror: https://mega.nz/#!JE1R3RhQ!MqY_OTyYrVM_DMOltiDfaZvTGZ8gCoUcATmOYEimM-U

3. You will need a complete firmware package of your desired Firmware. I recommend 9.2.0-20E/U/J.
Where do you get this package you ask? Well, Nintendo deleted all titles from their server older than 9.9.0-X, so you have to google it. I will help you to google it: http://bfy.tw/3Xqo

Cha0s Em3rald made MD5 checksum's for 9.2.0-20E/U/J N3ds/O3DS, check archive's checksum before using it! https://gbatemp.net/threads/md5-checksums-crc-for-all-9-2-update-packs.408114/

PLEASE NOTE: JP N3DS Users, you'll need to remove the 000400102002CA00 title from the download package in order to not get bricked! Do NOT install it!

4. Copy all firmware title .cia on SD Card:/update/

5. Remove smea's DNS, in case of unsuccessfull downgrade, you need in that case to start 3DS in Recovery mode to update and repair your system.

6. Start 3DS and go into Homebrewlauncher.

7. Start sysupdater

8. Wait for application to be ready. (ca. 1-5min)

9. Press Y to downgrade

10. Wait and pray until "Succeed. Reboot in 10 sec"

11. Done - Downgrade is (hopefully) complete!

I recommend to create an EmuNAND after downgrading and using a cfw Loader, like cakesFW or rxTools.


Q: Help! I have a blackscreen after the reboot!!!
A: Unplug SD Card, reboot. I think some SD data can't aren't compatible with downgraded titles, so delete your current "Nintendo 3DS" folder on SD card, if needed.

If it still doesn't boot, try to get into recovery mode, by pressing Power-Button to boot while holding L+R+Up+A, update and try again.

Q: sysupdater crashes/won't start/freeze.
A: (Hold L+R+DpadDown+B to return to Homebrew Launcher, then) start/reboot again. Some users needed over 30 attempts.
Try another hax; I used menuhax to start ctr boot manager.
TuxSH wrote that it can raise succeed boot of sysupdater if you started 3DS-FTP before and return with L+R+Down+B, then start sysUpdater

Alternative Way:
1. Backup/delete your boot.3dsx in sd root
2. Copy "sysUpdater.3dsx" to root and rename it into "boot.3dsx"
3. Plug SD card in and start hax (recommended: Menuhax)
4. *hax will load directly sysUpdater.

Q: What firmwares can be downgraded?
A: All firmwares up to newesest (10.3) can be downgraded. New 3DS is not confirmed because of no testing by TuxSH, but many users already tried and successfully downgraded their N3DS.

Q: I have an 2DS, which Firmware do I need?
A: Firmware for Old 3DS. MSET for 3DS can wants to move 3d slider after formating - you need to install only Firmware/MSET that was supported by 2DS, so NO 4.5! O3DS 9.2.0-20E should be fine, but not confirmed.

Q: It won't reboot after the finished downgrade.
A: What I did: Waited 10 minutes, then I powered it off. Downgrade suceed. You don't have another choice anyway.