If the trach is no longer for suctioning secretions or for ventilatory support with a respirator and if he is breathing easily, it may be possible to remove the trach tube quickly. If there is any doubt about it, however, the first step would be to replace the existent tube with one of a smaller size.
I don't know how much has changed since I last worked in a hospital, but I think if he is determined to be a candidate to wean, his trach would be plugged so many times a day for a specified amount of time. He would be monitored and tested to see how he is doing. The amount of time would gradually be increased til he was plugged all the time. If you ask an RN on his unit, they could tell you their usual policies. Hope it works!