Turn the thermostat to the lowest setting
Turn off power to the furnace
Turn off the gas control knob to the furnace
Wait 5 minutes for any gas to clear
Remove the furnace access panel
Set the gas control to Pilot
Press and hold the reset or pilot button
Use a long lighter or match to light the pilot opening
Keep holding the button for 30 to 60 seconds
Release the button and check that the pilot stays lit
Turn the gas control knob to On
Turn the furnace power back on
Replace the access panel
Set the thermostat to the desired temperature
If the pilot will not stay lit, contact a qualified technician