If you're referring to the half shaft, jack the car up and support it with jack stands under the frame or cross member, not the lower control arms. Remove the wheel and brake caliper. Hang the caliper by a piece of wire or support it in a way it doesn't hang by the rubber hose. Stick a screwdriver into the slots of the rotor to prevent it from turning, then remove the axle nut. Remove the brake rotor. Note the round holes in the mounting hub and the matching round spots of rust on the back side of the rotor. Scrape that rust off to prevent a brake pulsation and wheel wobble later.
Remove the pinch bolt next to the lower ball joint stud. Use a really long pry bar, (mine is 5 feet long), wedged between the cross member and lower control arm to pry the control arm down. The ball joint stud will slide out from the spindle. A little help from a hammer might be necessary. Pull the strut / spindle away from the car while holding the half shaft back toward the transmission. The outer cv joint will slide out of the bearing and hub assembly. It is helpful to first turn the steering system so that wheel is turned toward the center of the car. That will allow you to pull the strut out further. Pull the shaft out of the transmission. Some transmission fluid will likely leak out.
Put the new shaft in by reversing the procedure. When you install the axle nut, the tightness is critical. Use a click-type torque wrench to set the nut to specs. That will be somewhere between 180 and 240 foot pounds. Never place the weight of the vehicle on the wheel or bearing assembly before that nut is tightened. Doing so will make the bearing noisy.