Is it possible to Upgrade the 8120 with the software meant for 8100.
I would like to update my phone to ver 4.5 coz mine is on ver 4.2.

Any assistance would be appreciated.

Nope. You can only load 8120 software onto the 8120.

And here is a link to the 8120 4.5 software -> Latest OS: 8120 4.5.0.312/4.5.0.187 (Multilanguage)

thanks for the promt reply, and will get the correct software from the link provided.