The contacts should load automatically upon starting the car.
You can force an update by going to 'Office' then selecting 'Current Office" the press the 'Options' button on the iDrive controller
Under 'Current Office' scroll down to Update data' and select.
Or turn off / on Bluetooth on the same screen.
Wait 15 - 20 seconds and the contact list should start updating - watch the top of the screen for the process cycle indicator (spinning wheel).