First you've got to be sure that your EROM is CID52. If it's not, you'll have to upgrade the CID or choose different firmware.
Finalizing your phone=uploading a custpack to it.
Downloads - z310custpack - ALVA_Gen_CDA102669_2_R3A_GENERIC_CENT_EUROPE - Top Sony Forums <-- that's the custpack you need for CENT_EUROPE firmware.
Have a look at the XS guide in the tutorials section if you are unsure about the steps you need to take.