yeah my serpentine belts looks like it should be changed,is it easy to replace or not.also i have a 1998 a6 2.8

 

i do not thing it is difficult, all you may need is an appropriate socket and a long enough extension bar for comfortable leverage in dealing with the tensioner. i tried using the wheel not spanner but in my case the car was in service position which in your case you may have to deal with the tight space.

 

Like Kimi said, it is pretty simple. I believe it is 17mm socket. You just need a long wrench, about 18 inches or so. Loosen the tensioner and replace the belt. On my 2001, I just had to squeeze the belt out areoung the alternator and crank pulley, but wasn't that bad.