Ekf2 and PID values

I am thinking about changing the cycle time ekf2_main.cpp and PID values.
I’m analyzing mc_att_control.cpp and mc_pos_control.cpp for changing some part of those codes but it’s very complicated. PID values can change in QGroundControl I guess. Where can I start for this?
And what kind of changes can I make in codes? I’m thinking about changing control algorithm but I don’t have much time for this.