Samsung Galaxy S II has 3 main components ~ PDA, Phone and CSC. PDA == build version of the firmware, Phone == baseband / modem version and CSC == consumer software customization and it is 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. And you can change CSC if you have Multi CSC packages.
Note – this will factory reset your phone. Do backup before perform this task.