There are two limit switches on your garage door opener. One is the up limit switch and the other is the down limit switch. The down limit switch tells the garage door how far to go before it closes. The up limit switch tells the garage door how far to open.
Generally, the limit switches are located either on the side of the opener or under the light cover. Both switches should be clearly marked showing you if they control the up or down position of the garage door.
When you adjust the limit switch, you need to do it a little at a time. Turning even halfway can be the equivalent of a few inches. Turn the switch a small amount and then check the door to see how much further you need to go.