Hello,
Yes, I have the Tagus with the Onyx firmware.
First I recommended to backup your tagus firmware for the warranty...
To backup here you have some instructions (in spanish, sorry):
http://www.lectoreselectronicos.com/...l=1#post247875
Then update:
You have to download the 1.8.1 factory tools from onyx and flash it. It comes with an user manual for installing drivers and flashing.
After it, put the 1.8.2 update in the sdcard and apply the update.
Take care to pick up the C67 Carta firmware!
cheers