Reel mowers perform the same basic function as gas-powered rotary mowers---they cut your grass. However, reel mowers cut grass in an entirely different way than rotary mowers. They have a rotating reel that inches the grass against a stationary blade; this action cuts the grass in the same manner a pair of scissors would. Both mowers have the ability to adjust the cutting height. Unlike rotary mowers which have simple levers on the tires, it's a little more complicated to adjust reel push mowers' cutting height.
Loosen the bolt that holds the height of the roller shaft on each side. Most are held tight with wing nuts that can be opened by hand.
Remove the bolt out of the adjustment hole. Raise or lower the roller shaft to align a different adjustment hole. As you raise or or lower the roller shaft, you will notice that the bed knife on the front of the mower also raises or lowers. A higher bed knife means a higher cut, and a lower bed knife means a lower cut.
Put the bolt in the new adjustment hole to hold the roller shaft in place once you've adjusted the cutting height to your desired level.
Tighten the wing nut down to hold the roller shaft firmly in place. Cut your lawn at the new adjusted height.