Thank you for your question.
I can understand wanting to convert the range back to the Natural gas fuel.
Gas appliances are inherently dangerous and we suggest that you have a certified gas technician do the conversion from LP back to Nat.
The top burners have two different size orifices.
The two small orifices are part number 5303269527.
The two large orifices are part number 316010805.
You can purchase these orifices from:
Sears Parts Direct
The bake and the broil orifices are adjustable and you will need to turn the gas orifices counter clockwise a few turns to get them back to a natural gas orifice size.
You will also need to chage the pressure regulator back to Nat setting.
You will need to take the cap off the pressure regulator and tun it over and put it back on to return the regulator back to NAT.
I hope this will help.