See my thread on ATF change. I don't know what gearbox you have but it can't be that different, mine is a 722.6

http://mbclub.co.uk/forums/showthread.php?t=23969

I would recommend using only MB ATF. If you've ever done an engine oil change, you can do an ATF change. It will help to have a gearbox dipstick. Here is an image of the markings for the 722.6 box dipstick.

Please note that this dipstick may not be suitable for your transmission!