Garage door repair professionals may recommend cable replacement. Often the problems with the door starts with a broken cable and hence identifying it quickly keeps the repair costs to a minimum as you pay only for the labor charges. The faster you identify problems with the door, the lower are the associated costs.
You can call a local garage door repair shop to get replacements. They should have springs that will work with your garage door depending on if the door is for a single-car or double-car garage, or if the door is made out of wood versus steel. Usually both of your springs will have to be replaced for safety reasons. You should not replace the spring yourself unless you are a trained professional with the proper equipment because the springs are very dangerous and cause serious injury.
I have built many garage doors and installed many door openers. The typical garage door spring is not that hard to replace. I have to have 2 steel rods 1/2 inch in diameter to slowly tighten the spring.