Search the forums and look for a tutorial on the conversion, many people have done this on an A3, there are some caveats when changing from concert II to concert III, the antenna configuration is different and you may need a Y adaptor to fix the HF/ZF to HF/HF change on the radio. Also wiring adaptors, new buttons, trims etc. Most of the stuff is covered in the tutorials but these are basically for the Concert II to RNS-E navigation upgrade, the II to III upgrade just adds another level of complexity.