You are going to arrive on Level 3, Side A of MCO. You will arrive there, via a tram from the gate area. I am going to assume that you are tagging your bags and letting DME take care of them. If that is the case, when you get off the tram, you will be pretty much in the center of the terminal (actually you will have to walk past the outgoing security area before getting to the main terminal). If you look up, you will see neon signage that says either Side A or Side B. You want to head to Side B. Go down the escalators..which bring you to level 2, baggage carousel area. Continue going down (I use the elevators that are right there, on level 2 by the carousels) to level 1..ground transportation. DME is located past the rental car counters, all the way to the end of that area...they will be on the right side, with the outside bus area to your left (if you use the same bank of elevators I use from level 2).
It's very easy..even my directionally challenged husband can do it!!