I want to trade in my car how do I do it ?

When you find a car you like tell the dealer you have a trade in.

Be prepared to haggle with the dealer over the value of your trade just as you will for the price of the car you intend to buy. From a price perspective, the best deal is the one that is the cheapest when you compare the price of the new car less the trade-in you are being offered. This, however, does not account for other things like dealer reputation and consistency of options on the new car.