Samsung Galaxy S III firmware has 3 main components ~ PDA, PHONE and CSC. PDA == build version of the firmware, PHONE == baseband / modem version and CSC == consumer software customization (specified to geographical region and carriers). CSC contains the software packages specific to that region, carrier branding and also APN settings for data connection, MMS for your service provider. You can change CSC if you have Multi CSC packages like below example. By the way, only Samsung Galaxy S3 firmware with correct PDA, PHONE and CSC combo will get updated with Samsung Kies.

Note – This will factory reset your phone. Everything will be deleted. Do backup before perform this task.