I do not have the exact part number(s), however it appears you have to go OEM at the dealer since that vehicle is not listed in wiper blade aftermarket application guides. It appears your dealer is your only option.
The 1996-2001 Audi A4 has the most common hook-end wiper arms. See sources and related links below for installation videos. Also, purchase the replacement blades first and there will be additional instructions/illustrations on the replacement packages. Locate and press the tab or button where the wiper blade is inserted into the hook of the wiper arm and pull wiper blade out of hook. You may have to rotate and flex the blade to make enough clearance for the hook to pass through.
Need full make, model and year of the vehicle to answer this question properly.
You need a wiper arm removal tool. Look on ebay.
The Audi A3 has the newer, special "pinch tab" wiper arm attachments. Not all replacement wiper blades fit this type of attachment so be sure to lookup make, model and year of vehicle in book at store to ensure not only the correct lengths but also proper attachment. See below for pinch tab wiper arm wiper blade installation video.
That vehicle doesn't show up in aftermarket wiper application books so most likely its Audi proprietary. Most likely its super easy once you get the correct wiper blades. You could go to the link below and see if any of the attachments are similar or the same and then you'll have an idea. Then, off to the Audi Dealer for parts at a minimum (if you figure out the process) or possibly the entire service procedure...sorry.
Since I do not see the 2007 Audi A4 in my aftermarket wiper reference books, I'm assuming has proprietary parts. Most likely you'll have to go to the dealer and buy the part. Ask the counter person if the replacement comes with instructions. If not ask if they will provide instructions. If its a good dealer, they will help you with instructions. They'll also do it for you, but most likely charge.
Depends On Year - I looked up 2001 in the related link below, however you can change the year to the year of your A4 and look them up.
With a screwdriver
The 2003 Audi TT has 20 valves.
The 2003 Audi A6 has a V6 engine.
The 2003 Audi S6 has 40 valves.
The 2003 Audi A8 has a V8 engine.