Chinese Elms are subtropical and are able to be grown indoors or out. I prefer to keep mine outside during the summer and shelter them in an unheated garage during the winter where they will go dormant but still are protected from temperature extremes.
Being that you have been keeping yours indoors it has not begun the process of hardening off that is necessary to allow it to withstand the low temperatures of winter. So I would continue keeping it indoors though this winter. In the spring you can decide what to do then. You don't indicate where you are located, or if you have access to an outdoor growing area.
Spring is the usual time to repot into a free draining mix. You may be able to repot out of season though if you keep it indoors. The main thing that concerns me is that you don't know how much time has passed since its last repotting. For now it may be best to just concentrate on keeping it in good condition, pay particular attention to your watering, peat heavy soil retains a lot of water. Don't keep it soggy, allow it dry a bit between thorough waterings. A little bit each day is the wrong approach.