Check if the natural gas grill can be converted to propane use. This information is typically found in the instruction or owner's manual that came with the grill when it was purchased. If you are unsure, contact the manufacturer. The manufacturer can also sell you the conversion kit needed to complete the transformation.
Shut off the natural gas supply to the BBQ, then disconnect the gas line. Remove any front or side panels in order to have access to the BBQ parts inside.
Remove any orifices, regulators or gas valves marked for natural gas use. Replace them with the new parts compatible for use with propane. Ensure all fittings are tightly secured. Do not replace the panels yet.
Check for gas leaks around all the connections. Prepare a solution of soapy water by mixing dish soap with water. Turn on the gas supply, but not the burners. Pour a small amount of soap water around the connections. If bubbles result, there is a leak. Turn off the gas and tighten the connection.