Your flight will arrive on either the A side or the B side of the airport. DME is located on the ground level of side A. You will need to go to the A side and take the escalator/elevator to the ground level, where all the towncars, buses, rentals are.
Other posters are correct. You should have very succinct directions in your DME packet. In fact, I left it for my dh when he traveled with our dd last month. He found it with no trouble at all, and he's directionally challenged!!!