Add together the weights of the treadmill and the heaviest person who will use it. Find out if your floor on the second story will support this weight by consulting with the home builder or the building department of your local government.
If weight is not a problem, determine how the treadmill will be transported to the second floor. Measure the treadmill and the space it will have to go through. You will probably have to hire professionals to transport it safely.
Determine where you will place the treadmill on the second floor. Make sure you can connect it without overloading the circuits or causing a hazard with the electrical cords. Ask yourself if you will be able to look out a window or watch television while working out -- because you might get bored looking at a wall. Consider the option of placing the treadmill on a carpet, which may buffer the noise and vibration.
If weight, space and equipment transportation problems can all be solved, make the arrangements to get your treadmill in it's home location.