3. Extract image file, because I using Linux for all processes. So, I use xz tool to do that. (tar should do the same trick but my tar version just too old to do that and somehow I can't update it)
# xz -d BBB-eMMC-flasher-2013.09.04.img.xz
4. Now you need micro-sdcard + micro to sdcard adapter (and maybe sdcard to usb adapter in case that your pc has no sdcard slot) the image size is about 3.4 GByte so you need sdcard with more space than that.
5. Plug sdcard into pc and write the image to the sdcard with dd command.
*** note: replace (/dev/sdc) with your sdcard device. check it carefully if you don't want to lose your data !!
6. After a while, when dd command is done, try to mount the sdcard and explore it.you will see something like this.
7. Remove the sdcard and install micro-sdcard to the BBB. Remove all cables, hold "S2" Boot switch down while plug the power in. For about 2-3 seconds the user LEDs will flashing then it's ok the release the button. Now just wait... patiently
8. the user LEDs will flashing for about 30-45 minutes then they are all light up. That's mean the upgrade process was done. unplug the power and micro-sdcard.
9.Power on and go check to ID.txt file. If it shows the new firmware version then everything is well done.