I think I know what you mean - when you look at the phone under Bluetooth settings/my devices (or whatever your phone menu system has), it shows as audi huv 2342432423.
Anyway, as I said previously, I have the option to rename the device
displayed name on my Z600.
I guess from your reply that you are using the iPhone - I'm not at all familiar with the iPhone so I can't really offer any further suggestions.
[Time passes]
OK, I've just found the iPhone manual on-line and had a quick peek. It appears that the iphone does not have the option to rename paired devices within the phone. Bizarrely, it appears that the iphone can only be paired to one device at a time (and no, I don't mean connected). If you want to pair it with a second device - a laptop for instance - you have to unpair the first device before doing so. Wierd.
As for the Bluetooth unit in the car, I don't believe there is anyway of changing the name - so it looks like you are stuck with what you have unless anyone else knows better (which is highly likely around here

)