If you happen to have one of those old dial- or switch-type thermostats, it might be a good idea to upgrade to a programmable thermostat. A programmable thermostat is by far superior because it gives you complete control of your heating and cooling systems.
You can actually save a good deal of money by setting up programs on which your heating and cooling systems will run. This means they'll turn on and off automatically, instead running all day and costing you extra money. And, for example, you could set your heat to turn on a little while before you're due to arrive from work every day, so you're home will be nice and comfortable when you get there.
Removing the Old Thermostat
Obviously, before you install your new thermostat, you'll need to get rid of the old one. Start by shutting off power to the furnace/air conditioner at the circuit breaker. The cover of the thermostat should be pretty easy to pull off, exposing the thermostat's sub-base. Once the cover is off, you should see the screws that hold the sub-base in place; remove these with the appropriate screwdriver. Pull the sub-base gently away from the wall so you can see the wires. Loosen the screw terminals that hold the wires in place on the sub-base, and remove the wires.
TIP : There should be two wires connected to the thermostat: one red and one white. If that isn't the case, label the wires so you can remember which wire goes to which terminal on the thermostat.
Installing the New Thermostat
Installing your new thermostat is pretty simple. First, connect the wires to the appropriate terminals on the new sub-base (red to red and white to white). Then, drill new screw-mounting holes and push plastic wall anchors into the holes (these are to help the screws grip). Finally, screw the sub-base into place and snap on the cover (not forgetting, of course, to put in the batteries).
The tricky part will be figuring out how to use and program your new thermostat. As thermostats vary by brand, you're going to have to take care of this part on your own. Your user's manual will tell you everything you need to know. Once you've studied up, you should be able to easily set temperatures and programs. With the thermostat programmed to set the temperature and come on and off according to your schedule, you'll rarely have need to touch it. Just let it do all the work for you!