pictures?
Are they torsion springs (on a big pipe in kind of front upper of door) or tension springs (two on the upper sides of door)?
are you having back problem or is this a wooden/insulated steel double door (120+ #s)?
If you didn't did this before, call a garage door guy.
I did it , but I could lift the door: in steps, about 2 feet at a time, and place something under to hold in place (clamps on both side of track would be best or something wide like 5gallon paint buckets with lids on, stacked).
DO NOT USE JUST A 2x4, wood board: too much weight in one tiny spot.
Do you have somebody to help you?
If not, again, just call a garage door guy.