It is important for the freezer to be level. If it is not level, doors may not open or close properly and may not seal tightly. Also, drainage from the defrost cycle might be impaired as might the ice making cycle. The appliance was engineered based on it being installed in a level position. While there may be some tolerance for out-of-level installation, the appliance will operate at its best when properly leveled.
Before leveling, unplug the appliance to avoid an electrical shock hazard. Never tip a refrigerator or freezer, it is very heavy and can fall causing damage or injury.
Place a level on top of the freezer near the front. Do not put it on the door because the door may not be aligned with the freezer case. Check that the freezer is level from left to right. Also check that it is level from front to back.
If it is not level, adjust one or more of the feet until it is level. The feet are bolts that can be turned to raise or lower the appliance. If they cannot be adjusted with your fingers, use a crescent wrench or pliers.
If you have an ice-maker, it should also be checked for level after first leveling the appliance. It can be repositioned by loosening the mounting screws, adjusting it for level and then retightening the screws.