Special tools required:

WARNING: This page is about a different car, the 2006 BMW X5, 2005 BMW X5, and 2004 BMW X5. However, it is still accessible from the selected car via links, so may be relevant.

12 1 171
12 1 172

Necessary preliminary tasks:

Switch off ignition.
Remove all ignition coils. See Replacing ignition coil (N62) .

Unscrew spark plugs with special tool 12 1 171.

Installation:

Tighten down spark plugs with special tool 12 1 171 and special tool 12 1 172 (torque limiter).
Without special tool 12 1 172, observe tightening torque. See ENGINE ELECTRICAL SYSTEM - TIGHTENING TORQUES .
Tightening torque, see ENGINE ELECTRICAL SYSTEM - TIGHTENING TORQUES .

Fig 1: Removing Spark Plugs With Special Tool
Courtesy of BMW OF NORTH AMERICA, INC.