How to reverse updated galaxy s3?

[Tahir Khan2]

I have updated my galaxy sIII as below:
Firmware Details
Android Version: 4.2.1 ? JOP40D (Jelly Bean)
PDA: I9300XXUFMB3
CSC: I9300OJKFMB3
MODEM: N/A
Region: Middle East
Carrier: Unbranded
Changelist: 171637
Build Date: 19th February 2013
Download: I9300XXUFMB3_I9300OJKFMB3_ILO.zip

I want to reverse the update, i want to go back to origional 4.1.2.
is there any method to reverse my update?