Shut off the gas at the tank by turning the knob on top clockwise until tight.
Unscrew the large coupler on the side of the gas tank. The coupler is crimped to the regulator and fuel line attached to your grill.
Twist the couplers on the other end of the fuel line counterclockwise with pliers to remove them from the burner valves on the back of your grill's control panel. If you have only one burner, there will be only one coupler to remove.
Take the fuel line/regulator assembly to a hardware store or grill retailer to match the part with a replacement regulator. You can also order the replacement part from your grill manufacturer using the model number of the grill. The model number is typically printed or engraved on a metal plate on the appliance, usually on the back.
Fasten the large coupler on the regulator to the valve on the side of your LP gas tank, turning clockwise to seal the connection.
Hook up the connector (or connectors for two-burner grills) on the other end to the valve on the back of the grill's control panel and tighten with pliers.
Twist the valve on the tank top to release the flow of propane. Listen and sniff for leaks at the connection points. If you smell or hear the hiss of gas, shut off the tank valve and reconnect the couplers on both ends.