I did this on my 2010 Touran about 18months ago, Bit if a pain working out which aerial is which, some are built into the back windows, some are for satnav, phone etc and it depends on options specified when the car was built. In my case it turns out the shark fin on the roof was a plastic dummy! I replaced it with a dab roof antenna from a polo, I had to get a fakra cable from radio to roof at back, very fiddly, you'll also need a fakra 2:1 adapter because the head unit has 2 dab inputs but your antenna only has 1. Works well when done. Tried one of those window ones on my other car, a Citroen, didn't work but I found an adaptor that "converted" the existing roof FM antenna to a combined dab/FM and that works really well.