Edgar: First, I am no "professional" door installer. But, I just finished changing my torsion springs and didn't suffer a scratch. Here's a link to the article that got me on the right track.
There were a few things here and there that the article didn't prepare me for, but nothing much came of it.
I'm not sure what's really going on with your door, but on increasing the spring tension, I would refer you to the link and article. Depending on the age of the door/springs, I think replacement might be the way to go.
There is no "typical" project I've done around the house or auto mechanic/body shop that compares to manipulating these springs. Well, maybe the time I rebuilt the front-end on my '69 Mustang. Compressing those springs was kind of scary. But the tool did it's job and it wasn't that big of a deal.
I used 1/2 inch steel rod from Home Depot to turn the springs. There's nothing difficult about the project. I had no help. But, I'd recommend you spend 5 hours studying and preparing for the process before you begin. I guess this is one of those deals where what you don't know can definitely hurt you.