I installed a double wide door by myself. Also replaced the old extension springs. Old ones: one was rusty, one was stuck in the wall. So I also run a cable, after i took down in pieces the old door which had been rammed/hit hard.
Make sure you have all tools in place. all hardware. clear space to work. make sure you have the right springs and buy the safety steel cable. make sure you have the right loops.
have a helper, 3rd hand or gradual cut pairs of 2X4.
I used 5 gall buckets, as they where the size of one panel at a time.
i worked bottom to top, one panel at a time, lifted the whole door one bucket height at a time, then when up, clamp locking plyers on tracks, connected the cables.
I also used new rollers.
My test was how easy i could lift the door, when motor disconnected.
I re-used the existing tracks and motor.
Make sure you have at least 2 c-clamps or locking plyers to keep the door in place.
This is a case of SAFETY FIRST!
If you cannot lift a full door and have not at least qualified helper, and you have torsion spings, and everything said in the thread is strange to you, pay a good tech.