Remove the front seat belt upper anchor.
(Refer to Front Seat Belt - "Front Seat Belt Pretensioner")
After loosening the mounting bolts, then remove the height adjustor (A).
Tightening torque :
39.2 ~ 53.9 N.m (4.0 ~ 5.5 kgf.m, 28.9 ~ 39.8 lb-ft)
Install in the reverse order of removal.
Replace any damaged clips.