Or you can make your own from an old bank / AA / Tesco card.
I'm guessing you have the satnav stereo?? With two rectangular slots to each lower corner??
If so - cut the cards into two thin wedges say 5mm at one end going to 15mm at the other.
Insert the smallest end into each rectangular hole and then try and grip the radio and pull towards you. (not by the cards obviously).
If this does not retract the retainers, then try again after cutting a small part off the 5mm end (ie cut it off at say 7mm).
This worked for me when removing my Freelander OE system.
Regards,
Steve