Necessary preliminary tasks

WARNING: This page is about a different car, the 2011 BMW 328xi, 2010 BMW 335xi, 2010 BMW 328xi, 2009 BMW 335xi, and 2009 BMW 328xi. However, it is still accessible from the selected car via links, so may be relevant.

Disconnect BATTERY NEGATIVE LEAD. See 6120900 DISCONNECTING AND CONNECTING BATTERY NEGATIVE LEAD (E90) or 61 20 900 DISCONNECTING AND CONNECTING BATTERY NEGATIVE LEAD (E92) .
Remove airbag unit. See 3234020 REMOVING AND INSTALLING/REPLACING AIRBAG UNIT or 3234030 REMOVING AND INSTALLING/REPLACING AIRBAG UNIT (SPORT STEERING WHEEL)

Unclip decorative trims (1).

Fig 1: Identifying Steering Wheel Decorative Trims

Courtesy of BMW OF NORTH AMERICA, INC.