When purchasing your new vinyl replacement windows, always use the smallest height and width measurements you recorded. Otherwise, your window will be too large.

For a correct fit, the replacement window should be approximately 1⁄4 inch (0. 64 cm) narrower than the opening width and height. If your window measurements are in between sizes, round the measurement down. If your windows are an unusual size and a corresponding size of replacement window is not in stock at the home-improvement store, ask about custom ordering the vinyl windows.

Once you’ve removed the trim and molding, don’t throw it away. Save these items for later use. In all likelihood, your window will have 3 stops: one at the top, one on the left, and one on the right side of your frame. Not all windows have stops. If yours do not, don’t worry. In this case, you only need to remove the trim and moldings.

You can throw old weights and cords away, since your new window will come equipped with these items.

Be careful not to jam your chisel into the window frame, since you’ll install the replacement window in the same location.

Dispose of the old sashes once you’ve removed them from the wall.

If the tracks are held in place with screws, remove the screws using a Philips-head screwdriver, then pull out the tracks.

Caulk will keep the stool of the window from being damaged by water drops. It will also prevent drafts from entering your home.

Make sure that the sashes are still locked when you set the window in place.

If you don’t have a level, purchase one at a local hardware store. The tool resembles a metal bar that’s roughly 18 inches (46 cm) long.

Once the shims are in place and the window is square and opens and closes smoothly, snap off the shim stems.

If the ends of the shims stick out once you’ve screwed the window into place, snap them off.

The replacement window should have come with screws for installation when you purchased it. So, you won’t need to purchase these screws separately.

Insulation will block drafts and keep the window from letting hot or cold air you’re your home.

Work gently with the stops, since they’re relatively delicate and can break easily. If you do accidentally snap a stop, don’t stress. Find the right stop by bringing your window’s measurements to a home improvement store.