Overhead garage door springs, called torsion springs, control the tension of the garage door mechanism. If you are mechanically inclined and have experience working with garage doors, you can adjust the torsion spring in preparation for installing a garage door opener, or to simply reduce tension and make the garage door easier to open.
Close the garage door completely and attach a C-clamp to the door's movement track right below the lowest wheel to hold the door in place.
Stick a steel rod into one of the holes around the perimeter of the adjustment collar to hold it in position.
Hold the rod while simultaneously loosening the set screw in the adjustment collar. This screw holds the torsion spring in place, keeping it tense.
Turn the rod to move the adjustment collar. Turn it in the direction towards the garage door cable to tighten spring tension or in the opposite direction to decrease tension. Tighten in small increments at a time. When you have tightened or loosened your spring to your satisfaction, tighten the set screw to secure the spring and remove your rod.
Garage door springs are extremely dangerous and can cause serious injury when improperly handled. If you don't have experience with garage door adjustments, hire a professional to adjust your spring. Wear safety goggles, gloves and a hard hat when adjusting the spring to prevent injury.