Carefully move the washer out from its current location so you can access the rear panel. Make sure not to pull on the water pipes or the power cord.
Tip the washing machine back so the front legs are off the ground and put a wooden block between the bottom of the appliance and the ground. Turn the front legs counterclockwise equal amounts with an adjustable wrench to raise the front end before lowering it back to the ground.
Repeat the process at the back side of the appliance, tipping the washer forward and propping it up with a wooden block. Extend both legs by turning them counterclockwise equal amounts and lower the washer to the ground.
Place a spirit level on top of the washing machine parallel with the front edge and make a note of where the bubble floats in the vial; repeat the process a second time, placing the level parallel with one of the sides. The bubble should float between the markings in both positions.
Adjust the leveling legs, if necessary, until the bubble floats in the right position and then slide the appliance back into its original position.