To replace an idler arm, remove the old arm and bolts, remove the idler arm away from the centerlink, and then install the new arm. If replacing the Pitman arm, do it before putting the new idler arm on.
Jack up the car to gain access to the idler arm, and try to get it under the A-arm on the right. Remove the wheel on the right, and keep the jack there as a safety precaution. Remove the cotter pin from the idler's nut, and then remove the nut with a long breaker bar and socket. Remove the bolts that are fastening the idler arm to the frame.
Next, separate the centerlink and idler arm, which may be difficult. It is possible to use a Pitman puller for this, but it's possible this device may not fit on the idler. If it does not fit, try trimming the metal off of the Pitman puller to open it up. Put the bolt of the idler arm into the centerlink, and then put the new bolts into the frame, ensuring there are washers under the bolt heads.
Place the idler arm so the frame bolts go through the bolt holes, install the nuts and washers, and then torque to the specifications of the car. Install the large nut, tighten to specifications, place the new cotter pin, and finally finish by greasing the arm.