Connect the USB stick to the USB port furthest to the right of your console and start the console in recovery mode
Select option 6 (System Update), and follow the instructions that appear on the screen.
Once finished, enjoy the CFW 4.21.
Update: They have now released (via ps3-solution-pour-tous.doomby.com/blog/news-ps3/cfw-arch-4-21-finale-version-0-1-for-all-ps3.html) PS3 CFW Arch CEX 4.21 Final v0.1 for both PS3 Fat and Slim consoles (above) for those interested!
Stay tuned for more PS3 Hacks and PS3 CFW news, follow us on Twitter and be sure to drop by the PS3 Hacks and PS3 Custom Firmware Forums for the latest PlayStation 3 scene updates and homebrew releases!
Following up on their previous revision, today French PlayStation 3 developers Dev-Team-SPT / ARCH via arachetous have released PS3 CFW ARCH CEX 4.46 Build A01 alongside a demonstration video with details below.
To quote, roughly translated: Team SPT finally released the CFW ARCH CEX 4.46 Build A01 based on the Official firmware 4.46.
Compatible ReActPSN v2.26
Patched Peek / Poke
Patch Cinavia (protection removed)
Compatible with all original backup PS3 games
BD Emulation is OK
Support downgrade downgrade PUP by 4.25 to 3.55 Rebug or 999 or other (better to activate the menu QA flag first before installing the CFW)
Compatible Mini PSX / PS2 or Remaster Mini / Mini or PSP Remaster
Compatible with PS3 Blu-ray off (note: the reader must still be connected even if it is off).
LV0 patch to disable the check in ecdsa CoreOS
Installing from 3.55 or any CFW 3.xx or 4.xx
Compatible PS3 system has undergone a downgrade by a flash chip or dongle
Access to SEN ok (at your own risk)
Support QA menu flag if previously activated with toggle QA.
Various modifications of the XMB (RCO / XML Multilanguage)
Update the "Homebrew Tools" section (all the latest homebrew is rested 19 total)
Update the "Homebrew Manager" (includes all the latest versions of backup Manager)
Adding: Twitter Facebook connection and connection
Video that shows the modified classes and the use of ARCH Updater package RC6:
Nothing in the BD player console!
Do not install on a ps3 official firmware higher than 3.55!
Installing from the XMB or Recovery Mode (recovery option / 6)
It is strongly recommended to activate the menu QA flag from a CFW 3.55 Kmeaw or else if you've never done before (package: ps3-solution-pour-tous.doomby.com/medias/files/toggle-qa.rar)
Update your manager in compatibility payload 4.46
If you encounter a 800xxxxxxx error during installation, downgrade to 3.55 to go up on the 4.46 CFW.
By Team-SPT / ARCH
Thank you to the Beta tester! Thank you to Playgame6989 for its support.
ARCH Updater / Customizer package RC6:
For CFW 4.46: http://www.filefactory.com/file/4tqepxy4lnpd/n/ARCH_Updater-Customizer-RC6-for-CFW-4_46-only_pkg
For CFW 4.41: http://depositfiles.com/files/t809re9nk
For CFW 4.40: http://dfiles.eu/files/t809re9nk?redirect