Is it possible to upgrade the original 2003 Vogue head unit to a later version as in the 2006 models?

If so what is required?

No mate. The 2003 car is based on BMW electronics, cars after about 2005/6 based on Ford electronics. They just won’t work together as the network bus is all different.

You can get an android unit though, but it’s quite a bit of work to strip down and fit.

You can add Bluetooth to what you have using a BMW ULF from an X5 or 5 series.

 2011 Range Rover Vogue SE 4.4 TDV8

Previous cars :
2003 Range Rover Vogue TD6
1999 Discovery Td5 ES
1995 BMW M5 3.8 6 speed
1992 Range Rover 3.9 Efi Vogue
1992 BMW M5 3.8
1988 BMW 735i SE
1989 Ford Sierra XR4x4 2.9i
1981 Ford Fiesta Supersport

Thanks very much that clears my mind on that.