What's sad about this post is that you do have experience and choose to take the condescending and fear-mongering path. The name of this thread is "What are you doing today?" It fits in the mindset of this forum which is primarily a DIY crowd.I worked for, and had my own overhead door business for 15 years. I don't care what other people in this thread have said, and worked on tractor trailer doors or whatever. You need 2 springs, 2 winding cones, 2 stationary cones, and two 3/8" winding bars to do this job. You'll probably also need a spring gauge reader, and a conversion chart to tell you what other springs can be used if the ones you originally had aren't available. Before putting the new springs on, you'll have to "kill" the other spring that still has full tension on it. Then you'll have to remove the entire shaft and drums, put the new springs on the new winding and stationary cones on, and then put the whole shaft assembly back in place prior to winding the springs. And prior to winding the new springs, you'll have to know how to wind the cables on the drums, and then put a vice grips on the shaft to hold it with the tension on the cables, etc, etc... Call a professional to have the job done right. It'll cost you about 300.00, but it will be done correctly, and you won't be injured. And in overhead door vernacular, an "operator" is actually the "opener", and has nothing to do with the overhead door itself, other than opening it.
If you don't feel safe performing a task then by all means pay someone to do it. If you want to help out then please do. This post is not helpful.
Here's a real professional overhead door installation company owner letting his 5" 4" 115lb wife wrap the tension on a torsion spring.