WARNING: This page is about a different car, the 2004 Audi A4, 2003 Audi A4, and 2002 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Removing And Installing Securing Ring
Courtesy of VOLKSWAGEN UNITED STATES, INC.
Clamp drive flange with soft jaws in vice. Press circlip out of drive flange groove using new circlip -A-.