I noticed a few members asking how to go about flashing the official firmware that they downloaded from ASUS's site so I sent them off a request for a step by step guide for you guys, and here it is:
Thank you for contacting ASUS customer support.
To manually update your Transformer, please follow the steps below:
1. Download the most up to date firmware for your TF from the Asus support site from the link below:
2. Unzip the file and copy the “Asus” folder into the root directory of the Micro SD card.
NOTE: You can also copy the unzipped file to the /sdcard/ directory (internal memory)
3. Make sure that TF is on and the power cord is connected.
4. Insert the MicroSD card in the slot. Once MicroSD card is detected, a blinking exclamation mark should appear at the bottom of the main screen, next to the clock.
5. Tap on it in order to bring up the update wizard.
6. The update takes approximately 10-15 minutes to install.
ASUS Customer Support
If you are trying this because you cannot get an automatic OTA update, first try this.
Go to settings, apps, all
Find CMclient & DMClient
Clear cache, clear data & force close both apps
Reboot your TF
Go to settings, about tablet & check for update. Hopefully, the latest firmware will then download automatically for you.
A couple of points I feel should be noted:
MicroSD = The external Micro SDCard you physically push into the side of the TF
Copy the downloaded firmware onto the Micro SDCard while it is in the PC / Laptop card reader, before putting it into the TF (ie. Don't download the firmware on the TF or copy it to the SDCard while it is in the TF) as they state it will recognise the firmware once you insert the Micro SDCard back into the TF.
And remember it needs to be "UNZIPPED" before you copy it over
But it only needs to be unzipped ONCE. When you have unzipped it, there will be another zip file inside. Do NOT unzip that. If you end up with a META folder and a blob file, you went too far.
Hopefully this will help anyone having problems updating their firmware.
Some members have also reported success in simply copying the unzipped firmware (remember only unzip ONCE) to the /sdcard/ directory on the internal storage of their TF. This also appears to trigger the update.
The following post was made in TF300 help regarding the updating of the TF300 to Jelly Bean 4.2.1
Added by Edit by Janner43 - 28 February 2012
I came across the following PDF from Asus outlining this procedure which some may wish to save for a "rainy day"
Asus update SOP
Having obtained the latest firmware, members are advised to follow the advice in this Guide...
[GUIDE] How to update your firmware OTA - incremental changes & full OS updates.