my guess is thats its causing the door to go up crooked(pulling more on the side with cable attached. try pushing down more to that side and not in the center.. raise it all the way up to remove the other cable..tension will be less there.. but fair warning.. the door is gonna be heavy.. so be prepared when you go to close it..
Garage Door Installation
Well no it will not be to hard. They are called extension garage door springs replacement springs. The color on one of the ends is the weight code for the spring. Replace both springs! Those spring you will need the door open to replace.