The garage door torsion springs are located on a metal rod on the inside top part of the garage door. The tension needs to be adjusted when the garage door is not opening and closing properly. If either garage door torsion springs are not broken or worn, then they need to be adjusted. Adjusting a garage door torsion spring is a potentially dangerous thing to do if you are not careful.
Look at the torsion spring. There is a reddish cone on the left side of the spring that would be the side away from the centre of the garage door. Notice the screws and notches that keep it in place.
Take a metal rod that is about 18 inches long and ½ inch in diameter and stick it into the first notch to hold the cone. Make sure that the rod is firmly in the notch and able to hold the cone.
Use a 7/16-inch wrench to loosen the two set screws while keeping the rod in the notch of the cone. It is very important that you keep the rod in place since this could be the part that is potentially dangerous. If you take the rod out while loosening the screws to the torsion spring, then it could snap and hit you.
Place another rod of the same size into another notch on the cone. Keep one hand on each rod and turn the cone toward the right to tighten and toward the left to loosen the tension.
Remove one rod from the notch of the garage door torsion spring while keeping the other in place in another notch. Tighten the set screws. Once the screws are tightened, then you can remove the rod out of the notch and you will have adjusted the torsion spring.
Have someone help you get the tools you need instead of trying to do this job on your own. Make sure to perform this process for both torsion springs; otherwise, the garage door will end up uneven.
Wear goggles to protect your eyes. Do not remove the tension rod when loosening the set screws.