who: installed this? [complain to the installer: oops: you?]
what: you want is comfort within a degree or less.
where you live: climate and humidity and maximum insulation are needed.
when: now
why: comfort
how: money. maybe you are trying to run the whole house from one
thermostat?
you need to install at least one additional thermostat in the home and
have two zones with new motorized dampers directing the heat/cool to
the demanding zone(s).
see technical stuff at:
http://www.buildingscience.com/resources/