OTA on RA6M5

Hi everyone,
I am trying building a FOTA (firmware over-the-air) system using RA6M5 as master ECU and U2A as target ECU. I want to use CAN to connect master ECU with target ECU but do not know how to transmit image file through CAN. 
About master ECU and target ECU, refer image below:

Does anyone have resource or any idea.

Thank you for your support
Sincerely,
Dat Nguyen