WARNING: This page is about a different car, the 2004 Volvo S40, 2003 Volvo S40, 2002 Volvo S40, 2001 Volvo S40, and 2000 Volvo S40. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Open Socket Housing
Courtesy of VOLVO CARS OF NORTH AMERICA.
Open the socket housing secondary locking by turning the two rings shown. A "click" indicates that the secondary locking has disengaged.