Read the directions stamped on the valve handle sitting on top of the propane tank. Turn the valve in the direction designated as "Off" -- generally clockwise -- until it tightens to the tank.
Adjust the size of a spanner wrench to fit the nut connecting the regulator to the threads of the propane tank. Hook the spanner wrench on the regulator nut.
Turn the handle of the spanner wrench clockwise to loosen the nut. Tap the handle of the spanner wrench with a rubber mallet if the wrench does not turn by hand.
Remove the loosened nut from the propane tank by turning it clockwise by hand until it pulls from the tank.