How to upgrade Samsung Galaxy S3 LTE to Android 4.1.2 (manual update of UK Orange GT-i9305)

I've successfully upgraded my S3 LTE on the UK Orange network (EE / EverythingEverywhere) to Jelly Bean 4.1.2. The release features the funky multi-window mode from the Samsung Note 2, smart screen rotation feature, new Gallery layout, and even smoother Project Butter UI transitions, amongst other tweaks. I'm not 100% sure but I think this release may have improved the power consumption too, which is very welcome; I seem to have around 20% more battery available at the end of the day than I used to. But maybe I'm just playing with the phone less often ;)

Note my phone was already rooted with ClockWorkMod (CWM). See my earlier post for how I did that.

So, for JellyBean 4.1.2, I used the following EE ROM from SamMobile: http://www.sammobile.com/firmware/?page=8&view=10065

And in brief, here's how I did it.

• Backed up using CWM
• TriangleAway to reset custom binary counter
• Put into ROM download mode (VOL DOWN + POWER + HOME)
• USB hookup to my windows machine, ensure Kies is NOT running
• Use Odin3 to select the new Firmware ROM (the PDA section) and START
• Cross fingers!

The first 2 steps may not have been necessary, but they're what I did. Note the phone will no longer be rooted after update, and will be back to stock recovery mode (No CWM installed). Modem is still fine and makes calls, accesses VoiceMail, Internet etc. Also, all my apps, settings, customisations, data and media files remain unscathed. Woo, yay, hoopla.