How to Change the Legal Representative (Admin-c) of a Domain name

To change the Legal Representative of a domain, or rather change the Admin-c (Administrative Contact), you need to send specific information which varies depending on the type of extension of the domain name
     
     -   Change of Admin-C of .it domains 
     -   How to Change the Admin-C of a .eu domain name  
     -   How to Change the Admin-C of domain names with different extensions to .it and .eu