Swapping RNS 310 with RNS 510 - Bluetooth functionality

[jacke]

I'm about to get 64 plate passat next week and I will think about changing RNS 310 to RNS 510 (screen size matters ). Currently installed unit comes with nav, bt and DAB, but when I was looking for 510 on ebay I only found units with DAB (no info about BT). So my question is: is the BT module installed separately to the head unit or this should be RNS function?

[UMEL]

Google 'VW where is the BT module', and it's under the front passenger seat.