I was able to do this earlier this year by removing the rear center headrest so I would have room to work, loosening the headliner at the center of the rear window and reaching in with a cresent wrench set by the nut on the replacement antenna. The only fun I had was getting the nut started on the new antenna and figuring out how the connector worked. Assuming you also have a Jetta sedan and that your arms aren't too much bigger than mine I suspect you can pull this off the same way. I was surprised by how much better my AM reception was once I replaced the antenna, so my amplifier must have been dead for quite a while.