Removing and adding tension are not the only dangerous parts to the process. With larger much stronger high cycle springs it could be too much and cause the door to shoot up like a rocket the second the second the set screw is tightened after putting tension on the new spring. Always clamp the door down befor added tension to be safe. I've replaces 1000's and 1000's pairs of springs over the past 12 years in the garage door business. If you run into anything you don't understand I can probably explain it to you. How did you measure you wire diameter on the existing spring to give to the guy calibrating the new springs?