Locate oil filter of Audi A4

If you look at what seems to be the oil pan. There will be a round plate on the bottom with I think allen wrench screws. It's in side that. Hope this help!

2006 Audi Quatro V-6 Oil Filter

In order to service the oil filter you must remove the coolant resevoir and lay it aside- remove oil cover with SW 36-2 clean sealing surfaces on oil filter cover and at oil filter housing

Sealing ring on cover replacing:
remove sealing ring at pull tab- insert new sealing ring with semi-circular profile in groove- the pull tab must face upwards- smooth side of sealing ring must face towards outside- be aware that this seal can be installed inside out which can cause a leakage

engage new oil filter insert into oil filter cover- reinstall colant resevoir