Your Mazda 6 has coil springs instead of leaf springs in the suspension. Some Mazda 6 owners replace the coil springs for maintenance reasons; others replace the factory springs with special lowering springs to give the car a "performance" look and lowered center of gravity for more stable handling. These steps address removing the rear coil springs from a Mazda 6.
Lift your Mazda 6 and support it by the frame with safety stands and remove the wheel nearest the coil spring you intend to replace. Use a jack to support the lower control arm, releasing the pressure from the coil spring. Remove the lower link side rear stabilizer bar bolt.
Loosen the inner bolt of the rear lower control arm and remove the outer bolts, then slowly lower the control arm and remove the coil spring. It is vital that the coil spring not be under tension when it is removed; the sudden release of the stored energy could result in injury or death.
Inspect both upper and lower spring seats for signs of wear and replace them as necessary, then install a new spring into your vehicle, making certain that it firmly seats and is oriented with the small outer diameter side down.
Raise the lower control arm into position (using the jack) and install the lower arm bolts, tightening the outer bolt first, then the inner bolt, to 63 yo 86 foot pounds of torque.
Reinstall the rear stabilizer link bolt and tighten to 31 to 44 foot pounds of torque. Reinstall the wheel you removed in Step 1 and lower your vehicle to the ground.