To lower the spare tire on a 1997 Mercury Mountaineer you first have to deal with the winch mechanism which holds the tire in place. Inability to lower the tire probably is caused by the manner, in which the manufacturers secure the tire, in a such a way, as to prevent the winch tube from rotating. This has to do with the cable that supports the spare tire.
I located a website, I believe could be what you are looking for. If, you go to www.accessconnect.com you may find what you are looking for. I would suggest, however before you do anything go talk with a mechanic working in a Mercury dealership to learn, if, the information on this website can resolve your problem and not create a new problem. Changing the position of the spare tire could cause a different problem, so check with a mechanic first. Good luck!