HI I want to change a thermostat.I just bought noma programmable thermostat.Right now I have installed just regural termostat for my AC and heating system. The problem is that my old termostat installed has 4 wires and noma thermostat has only two wires. Can anybody help with this how to change thermostat?

Take the Noma back. They are junk to start with and you also have the wrong kind of thermostat.

Get a Honeywell for heat and cooling.

Follow the directions exactly as Honeywell has them listed in there instructions and do not disconnect any wires till you have the new thermostat. Label all wires and there location on the old thermostat before you remove the old wires.

Definitely take back t-stat.