Assuming your google-search-like post means that the new thermostat has two wires and there are four wires coming from the furnace for the old stat, and that you have a gas forced air furnace, I would say hook up R and W to the new stat, and disconnect the other two wires at the furnace. If this doesn't help, help us help you by posting more info.
What is the new thermostat? Some of the fancy new ones only use two wires to communicate with an at unit board which then tells the furnace what to do. Or you may have a high voltage thermostat which only uses two wires.
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