Each door is different — some need to be taken out when they are in the up position and some when they are in the down position. If a door has tension springs on them, it should be taken down when it is in the up position. It is very important that there is no tension on the door when taking it apart.
Once the door is up and locked into place there is no tension on the spring and it is safe to release it.
Keep in mind that when the springs are released there is nothing to help with weight replacement. Garage doors weigh 150 pounds or more and if the door were not locked in place, there would need to be some way of holding it up until it can be lower manually. If no one is available to help, a clamp can be put on the track at the end of the door (Image 1). When ready, release the clamp and take the weight of the door.
Remove the tension spring cables and then carefully put the door down (Image 2).