Also, slice through any paint covering the seam between the parting strip and the jamb, using a putty knife or chisel.

If you can only work inside, pull free one of the parting strips - the molding that divides each side of the frame.

Reinstall the outer molding or the parting strip, then attach the lower sash by following the same procedure.

Unfortunately, the parting strips are usually inset in a groove cut into the window frame.

To remove the parting strips, first remove the lower window sash.

If you must work from indoors, use pliers to pull free a parting strip - the molding that divides each jamb down the center.

Do not remove the parting strip spanning the top of the window frame.

To free the upper sash, you'll have to remove the parting strip between the two sashes.

If the instructions with the replacement channels specify, use a sharp chisel to shorten each end of the upper parting strip by a half inch.

Each should operate smoothly when pressed gently against the parting strip.