"IF" it is a VDO speedo, the instructions are here:
http://www.nsifleet.com/pdf/ProgrammableSpeedometer.pdf...but it may not be one. Mine (2004 4/4) looks very much like a VDO though I haven't tried checking it (turn on ignition while holding in button) yet. Most modern speedos are electronic and can be programmed, they get their signals from a gearbox sensor and they count pulses per mile.
