Hi my 2017 Audi A4 ultra model doesn’t have apple CarPlay , it also only has 1 usb in the glovebox . I was wondering if I bought a infor screen from a breakers yard with apple car play would the screen be a straight swap over .  Or is there more involved . I was hoping that it would be basically on plug 1 screen and plug in the other 

I'd be very surprised if a screen change alone made a difference. 

You would need to get the mmi unit - probably in the glove box.

It can be removed like an older car radio but the next problem may be that you need to get the mmi unit paired to your car (or you might need the smartphone interface) normally through audi or some 3rd party companies like Hazzydayz - it might be cheaper to go to them and get CarPlay sorted. 

Thanks for the response. I’ll probably go with the Units they are selling on AliExpress . Seems to be easier & going by reviews all are pleased with how they worked out