Dishwashers can be leveled by adjusting the hex nut up or down on each leg.
More Info: You will need a level to find out how uneven the dishwasher is and to check it as you adjust the legs, and you'll need a wrench that fits the hex nut or an open-ended crescent wrench that can be adjusted to fit. Turning the nut counterclockwise raises the leg and turning it clockwise lowers it. Adjust each leg up or down until you see the right level reading from both front to back and from side to side.
Close the door and place the level against it. To level the front legs, push up or have someone else push up on the dishwasher so you can more easily turn the hex nut. Check level from side to side by opening the dishwasher door and putting the level on the top of the front opening.
If you have trouble with the legs or if the nuts won't move as far as they need to, you may need to use wooden shims to hold the dishwasher in place. Once you're sure which legs to put them under, hammer them in until the dishwasher is level, then remove any extra wood that protrudes. Use the level to be sure the dishwasher is even. If it tips forward even a little, the dishwasher may leak.