How do you change a thermostat that has 6 wires but the new thermostat only takes 5?

It is not what the thermostat needs, but what your HVAC system needs from the thermostat. You have it identify what it needs and then figure out how to make the 5 terminals of the thermostat do the job. See https://www.askmehelpdesk.com/heating-air-conditioning/common-thermostat-questions-40771.html Also see https://www.askmehelpdesk.com/heating-air-conditioning/read-before-you-post-question-40767.html and https://www.askmehelpdesk.com/heating-air-conditioning/best-results-read-first-38671.html