Do not try to remove the extension spring that is not broken when the garage door is closed.
How to install garage door extension springs.
Since extension springs are determined by how much weight they each lift and the pulley system cuts this in half you need to replace your old springs with 200 pound extension springs.
The new spring s diameter length and wire size or gauge must be the same as your old spring.
Replacing garage door extension springs is not a difficult task provided you know all the key steps.
Granted garage door spring installation work requires time and attention so it is best to save the task for the afternoon of a free day.