The thermostat controls the heating and cooling in homes and businesses. Newer thermostats can be programmed, while older thermostats cannot. Choosing between manual or programmable thermostats will depend on whether you'd prefer to set a certain temperature for certain times of the day or prefer to manually change the temperature.
Determine what kind of thermostat you have, whether it is manual, digital or mechanical. Manual is the simplest and will have a lever on top or on the side of the box. Digital will have numbers, including temperature and time. Mechanical are mostly circular, but sometimes rectangular, and will have numbers without the time or date.
Remove thermostat cover. You may have to remove the screws with a screwdriver, or you may have a thermostat that allows you to pop off the front cover without using any tools.
Check to see if the mercury is level. The mercury is a liquid inside a glass vial that conducts electricity and flows like water. It will need to be leveled in order for the temperature to be accurate. If it isn't balanced, push up or down on the side of the vial that has more liquid in it in order to get the vial to level off. If it continues to go off balance, you may need to replace the unit.
Push the lever up or down. If you have a manual thermostat, you will not have the ability to program it. Therefore, there will be a lever on the side or top of the thermostat, and you will need to push the lever up if you want it warmer and down if you want it cooler.
Program your mechanical or digital thermostat. You will have an option for the temperature you want set for a specific time and date.