Window blinds are raised and lowered with the help of cords passing through a cord lock installed in the head rail of the window blind. The cord lock "locks" the cord in place to hold the window blind in a raised position. Pulling down on the cord and then to the right locks the cord. Applying a slight amount of downward pressure on the cord while moving the cord to the left unlocks the cord and allows the blinds to lower. Open the cord lock in your window blinds to replace them if necessary.
Remove the window blind from the brackets that hold it in the window. Depending on the type of blind, the head rail either pops from the brackets, or a cover snaps off the bracket to release the head rail.
Mark the knot locations on the window blind cords, using a pencil. Untie the knots in the blind cords. Remove any decorative beads from the ends of the cords.
Access the cord lock through the open top of the head rail. Pull the cords up through the open cord lock inside the head rail, removing the cords from the cord lock.
Pull the open cord lock from the head rail. Use a slotted screwdriver to pop the cord lock out of the window blind head rail if necessary.