You will need to lift the car (ramps or jack) to access the drain plug. The transmission pan will be black and the plug will be on the bottom unlike an oil pan plug which drains from the side. I can't remember the bolt size, but someone will. Probably 14mm.

Take the plug out and then put it back in after it drains for a few seconds. There will be some mess, but to me it would be a small price to pay to have the correct fluid lever.

Idea 2- Since its winter and you are unfamiliar with the car, take it to a jiffy mart and ask them to just drain a quart. Probably wouldn't charge you more than a few bucks.

Good luck

ps- dont know if its already been said, but to check the dipstick IS a little tricky sometimes! You need to be reading where there is a DEFINITE line of fluid on the stick. One side of the stick will occasionaly show a ("blotchier") higher mark than the other because of the way it contacts the internal walls of the tube.

__________________
'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E