I replaced both the drive belt as well a the walk belt on a NordicTrack A2550 in Turner, Maine this past week. This in my opinion is one of the worst models to perform this task on, due to the method used to secure the front (drive) roller.
The front roller is held in place on both ends by a bolt that passes through two sections of the frame and then into the end of the axle shaft. This bolt assembly also attaches the front part of the frame to the rear part of the frame which virtually holds the two treadmill sections together, as well as secures the front roller in place.
In short changing a drive belt, walk belt or front roller on this model is a virtual nightmare and a poor treadmill design in my opinion.