If one garage door spring breaks do I have to change both?

Absolutely! Extension springs (located on either side of the door) need to work together and in sync in order for your door to run smoothly. If one is pulling too much and the other not enough the door will wobble or not go up and down at all. Unless you truly know what you are doing, DO NOT attempt to change you springs yourself. Springs (extension or torsion) hold an enormous amount of tension and one mistake can cause bodily harm.