look down from the top with a flash light you will see a small wire around the end nearest the radiator. That is the clip pull it with needle nose or pry it whatever. Then wiggle the tube from side to side as you pull it off. It's not going to just pop off for you. Sorry I don't have pics. Keep in mind they have all sorts of tubes coming off them that have spring clamps as well. Use a pair of pliers or I use a pair of vise grips with good teeth to open them and slide them down the hoses.
02-A6 Quattro 3.0 Avant
00-A8 Quattro 4.2