Looking at your current wiring it seems you have single stage heating only and no AC. Is that correct? You also have a C (ground) which is required with the new thermostat. This should be a easy swap of disconnecting of the four wires and reconnecting to the same letter terminals on the new thermostat. You need to read directions about setting the thermostat for heating only. It may already default to the proper setting but you should verify this.

Before you do anything, shut off the power to the furance. Most furnaces have a power switch located nearby. Otherwise you will need to shut off the circuit breaker.

Correct, this is a heating only, no AC. Thank you for the comment and guidance.