For this, we would suggest you walk into the nearest authorized service centre as they will be the better person to assist you. You can click on the following link to see the details of the nearest service centre and selecting your city accordingly - Service centre
As of now, TUV 3OO is offered with a BS4 engine. However, Mahindra is planning to introduce the BS6 engines soon enough. Mahindra XUV300 is all set to get and BS6 engine and others are lined up as well.