Originally Posted By: Hokiefyd
If these are the tension springs that attach to each side of the door, and also back at the opener mounting point, then they're pretty easy to replace yourself. As I recall, they are color-coded for the correct spring rate. Or, there are online guides to help you figure out which to get, depending on door size, door weight, etc.
I have two 8' aluminum garage doors, and replaced all four of my springs a few years ago. One had broken and one was real saggy, so I just did 'em all. Remember to run the safety cable down the center of each one, so when it eventually breaks again, the spring is contained.
If they're the torsion springs that mount across the top of the garage door, along the front wall, then I wouldn't do those myself (I understand they're more dangerous for a DIYer to do).
This is the correct post. Home Depot and Lowes sell the springs. Look at your existing spring for a whiff of paint on one end, you can also take the broken one with you to the store as the diameters differ based on rating. It's not hard to change them out. Not dangerous. Uncouple the garage door opener if you have on, open the door all the way and use a 2x4 to hold it up while you change out the spring(s). The single spring mounted above the door is dangerous.
There are DIY guides on line.