Remove the old hinge with the screw gun. The old hinge is connected to the attic door. Hold the door with one hand and use the screw gun to unscrew the hinge with the other hand. Move the door out and put it off to the side for now.
Use the pliers to remove the old spring. Use the screw gun to remove the old hardware. After removing the old hardware, clean the area where you will be replacing the new spring. Attach the new hardware with the screws that came with it.
Add the new spring. Pull the ladder fully down because the new spring will need to be attached to the attic floor first. Lay the spring along the line of the steps so you can measure where it will be placed to the opening. Use the tape measure to measure this. Now the spring should be extended so reach down to make sure you can fold and unfold the door.
Mark with a pencil or marker on the attic door where the new spring should go. Also mark on the attic ladder where the other end of the spring should be placed. Make sure you are fitting the spring the right way. It should extend outwards over top.
Use the screws that came with the new spring and the screw gun and screw the screws tightly into the marks you made on the attic floor. Fold up the ladder and screw the new spring on where you marked on the attic ladder. Repeat this on the other side of the ladder and test it to make sure it folds and unfolds like it is supposed to. If not, adjust the ladder as needed.
Re-install the door now that the ladder is in place. You re-install the door with the new hinges.