You should have a drain plug like what is shown in the center of the pic. You can take a long box end wrench to turn and you will have to reach it from underneath. Mine takes a 19mm and I use a long box end wrench on it. I removed the head to give you a better shot
. This is the E320 engine but yours should be in about the same location - around the vicinity of the 5th cylinder on the passenger side about 1/2 way down the block.
Do a search on refilling - you have to try to get all the air out of the system which takes some doing.