Turn A-C/furnace OFF;
Mark/Tag EACH wire conductor end BEFORE disconnecting any;
Mount new thermostat backing-plate;
connect each wire to new thermostat according to marks/tags;
Turn A-C/furnance ON & test.
Buy a digital thermostat. Take apart your old thermostat. Look at how the wires are connected. Make a diagram if necessary. Open new thermostat. Read the directions. Install it using the directions in the package.
Changing to a digital thermostat has never been easier. The color coated wiring in the walls of most houses is standardized, and is easy to match up on the new one. You usually need only a screwdriver.
You are going to have to take the old one off the wall. You will have some wires going to it and just take one wire off at a time so you know where it goes on the new thermostat.
