Are you referring to the brake rotor? From the picture, it look like you have already removed the caliper. (The caliper is the component that contains the brake pads)
If you mean the rotor, yes, you need to remove the wheel spacer by removing the 5 bolts in between the wheel studs on the wheel mounting surface to remove the rotor.
Ultimately, if you are trying to remove the axle shaft to be able get enough room to remove the ball joints on the knuckle you could do that without removing the rotor by removing the three 12 point bolts on the back side of the knuckle that hold the unit bearing to the knuckle to slide out the axle shaft.