How can I get start with pixhawk?

Hello everyone,
Im begginer.
I have a tilting arms quadrotor.
The quadrotor is controlled by pixhawk 1, while the servomotors which rotate arms are controlled by arduino MEGA.
As arms chage position, the center of gravity change and the inertia matrix change too.
As a first step I want to change the inertia matrix in the pixhawk firmware then change the allocation matrix.
Please, what are steps to do in order to achieve this step.
Thank you in advance.