Disconnect the spark plug boot from the spark plug, typically located on the front of the engine. This will prevent the mower from accidentally starting while you raise the cutting height of the mower deck.
Locate the height-adjustment levers on each of the wheels. Depending on make and model, walk behind lawn mowers can have one, two, or four height-adjustment levers.
Unlatch each adjustment lever from the notch for its current height setting. Push each lever forward or backwards to raise the lawn mower's deck higher off the ground. Refer to your owner's manual for specific height adjustment directions.
Ensure each adjustment lever is secured in a new notch for the higher setting. Check that each lever is adjusted equally to the same height setting.