If you look at each side of the unit at an angl,LH side from the right and vice versa, you should see two half hidden holes on each side going at an angle away from the centre of the unit, standard removal tools will do the job.
If there's still nothing visible there may be a trim or trims you have to remove to access the holes.
When it's removed you may find that the car has a BMW wiring loom for which adaptors are available. You'll most likely need an antenna adaptor too. If you need both then about £15 should cover it.
Steering wheel control adaptor will take the place of the BMW loom adaptor (if reqd) but will need a brand specific patch lead. Please bear in mind that not all brands are compatible with OE wheel controls and in many cases functionality is limited.
Good luck. :)