Depending on the height of the vehicle parked in your garage, mark off two wooden boards using a lead pencil and a tape measure. Normal cars range from 60 inches to 70 inches in height. If you drive such a car, mark off each wooden board at 78 inches. Saw off excess part of the board with a circular saw. Place these 78-inches-high wooden boards on both ends of the garage. You will be using these boards to brace the raised garage door.
You will never be able to lift open the garage door while the door opener arm is in its correct place. Detach the arm from the door-opener rail by pulling the emergency cord downwards.
Now you need the help of an assistant. Position yourself at one end of the door and ask your helper to go to the other end. Make sure that both of you have a pair of vise grips handy. Insert a pry bar under the door and ask your helper to do the same at his end. On both ends of the door, place a piece of scrap wood on which you will rest the door before lifting it. Make sure that the piece of scrap wood is high enough to allow you to get your fingers under the door.
Now you and your helper should push down simultaneously each pry bar. This will lift the door a little bit. While maintaining the pressure on your pry bar, carefully slide the piece of wood scrap directly under the door. Ask you helper to do the same. Slowly release the pressure on the pry bars until both ends of the door rest on the pieces of scrap wood that you slide under the door. Set away the pry bars.
Carefully lift up the garage door, asking your helper to do the same. Remember to lift the door simultaneously, keeping it even to prevent it from binding in the tracks. Keep lifting the door until you can brace the door with the 78-inches-high wooden boards. Remember to position each wooden board perpendicular to the garage door.
Secure the door in place by clamping it with a pair of wise grips on both ends. You can now safely move out your vehicle from the garage.