I have a 1998 2.8 V6 Audi A4 and would like to know how to change the oil.
Thanks,

 

Remove the belly pan, if it's still there, remove the oil drain plug and collect old oil, carefull, it may be hot. Remove the oil filter, replace with new one (from auto parts store, they can also tell you how many quarts oil your model needs). With drain plug in, filter on, put about 5 quarts 10W-30 or 5W-30 in, run engine for several minutes. Then check on level ground the oil dipstick, top up to Max on stick as necessary.
Oh, dispose/ recycle the used oil, it's poisonous so don't pollute the environment. If you need more detailed instructions, use the search feature, I'm sure there are lots of articles on this topic.

Adding to your other post: Bentley Publishers sell good service manuals for all cars, I use mine all the time