Thanks, WVICARY. I just discovered that my engine(V6/3.2) has a Serpentine belt auto tensioner. There is no need to remove the engine. The procedure is as follows (V8 and TDI engines might be different.)
1. Drain the engine coolant.
Remove or at least loosen pulley bolts
2. At the auto tensioner (located above the water pump), turn the wrench(17mm) counter clockwise as shown in the first picture and release the belt. Make sure you remember where everything goes when you put the belt back in.
3. Unscrew pulley bolts (second picture).
4. Unscrew water pump bolts (located behind pulley).
5. Remove old water pump.
6. Install a new water pump.
My local car shop, not even a VW dealer, quoted me $500. I found out that it's not difficult at all, so, I'd rather do it myself.