Adjusting Garage Door Springs

adjusting garage door springs
How can I adjust the tension of my up and over garage door with spring Henderson generals?

At the end of spring there is a cap that has two allen screws that close on a shaft to maintain tension in the spring.There is also a hole in the lid. I insert a screwdriver into the hole to support the tension then undo the screws Allen and wind in some more tension and tighten the screws