Remove the upper B-pillar trim panel

NOTE: Description is for left component only. Procedure on the right side is identical.

Fully position the front seat to the front and top.
Loosen screw (1).
Remove end fitting (2).

Courtesy of BMW OF NORTH AMERICA, INC.
Release the B-pillar trim panel (1) from the clips (2) and guide it downwards out of the headliner.
Remove the B-pillar trim panel (1) and, when doing so, guide out the seat belt.

Courtesy of BMW OF NORTH AMERICA, INC.