Immobilizer and Radio Codes

I have been the proud owner of a 2004 C220 CDI for just over 2 weeks now. This is my very first Merc and it is the most modern car I have owned!! I understand that if I want to replace the battery I must first access the immobilizer and radio codes. Can someone pleae tell me where I may find these details. I do not have all the manuals for the car - only the main user guide.

Thanks