How to replace spiral balance
Things You'll Need
Raise the lower window sash 5 inches from the bottom of the window sill. Unlock the lower window sash and tilt the top of the sash into the room. Grab the sides of the lower window sash and angle one side up to disengage the sash from the shoe and remove the window sash from the window.
Remove the vinyl covers on the inside of the window frame that cover the window balance. The vinyl covers will pop off when you pry them with a flat-head screwdriver.
Grab the bottom of the spiral balance with the special balance-winding tool or a pair of needle-nose pliers. A balance winding tool is specially designed for removing and winding the spiral balance. It works like the jack-winding tool on some automotive jacks.
Pull the bottom of the spiral balance out of the shoe inside the jamb and slowly allow the spiral to unwind. If using a pair of needle-nose pliers, use both hands to hold on to the pliers and rotate with the spiral counterclockwise.
Remove the screw that secures the top of the spiral
balance tube to the top of the inside window jamb, using a Phillips-head screwdriver. Pull the window balance out of the window. Measure the tub portion of the window balance with a tape measure and make sure your replacement balance is the same size.
Insert the screw that comes with the new balance into the holes in the top of the window balance tube. Secure the top of the balance to the inside top of the window jamb with the retaining screw and a Phillips-head screwdriver.
Grab the lower end of the window balance with the winding tool or the needle-nose pliers and pull the spiral down. Rotate the spiral 12 times to apply tension and insert the spiral into the shoe inside the window jamb. The upper pins on the end of the spiral will fit into the shoe.
Snap the covers back over the inside window jamb with your fingers until the covers lock into place. Set the bottom of the lower sash into the shoes on each side of the window frame and position the top of the sash into the frame until the sash locks into position.Source: ehow.com