How do I rescind ITIN and update with SSN for minor?

Dear experts:

How do I write a ITIN rescind letter and update with SSN for my minor son? Can I sign the letter on his behalf and send all info to the following ITIN operation department?

 

Internal Revenue Service
ITIN Operation
P.O. Box 149342
Austin, TX 

 

Any insight would highly be appreciated.

 

Regards,

Shyam