Select IMU - set rate

Hello everyone,
I am new with ardupilot. I cannot find how to select the imu used to get data (mpu9250 or lsm…) and how to set its rate? I am working with Navio2+Raspberry3. The Raspbian Emlid image has a pre-installed Ardupilot.
Maybe you can find what you need here. Seems that the ardupilot+NAVIO2 use mpu9250 as imu. Use hmc5843 as second compass. On here, it looks like the LSM9DS1 has only the sample program with C++ and is not used in the ardupilot.
And i donnot think you can change its rate. (At least I think so, maybe someone else has a way)