Outside the house, use a razor knife or chisel to cut away the caulk and sealant around the window to be removed (Image 1).
Inside, use your knife to score the edges of the casing all around the window, which will prevent the paint and drywall paper from pulling away when you remove this trim. Use a prybar to lift and remove the interior casing (Image 2).
With the trim removed, along with any insulation tucked in the gap between the window and house framing, you’ll see the nails or screws that hold the window in place. Use a reciprocating saw or hacksaw with a metal-cutting blade to cut all of these attachments (Image 3).
Remove the window by having one person push from the inside while one or two helpers on the outside catch the window as it comes free. Even small windows are heavy, so be cautious and be prepared. If the window sill height is low enough, set up sawhorses or a scaffold to “catch” the window onto as it comes out.
Before installing the new garden window, find and mark the center of the window opening. Also determine the installation height of the garden window, which may be different from the old window and the rough opening, and mark a level line across the opening.
If the rough opening is taller than needed, it’s generally better to install the new window to the top of the opening and fill in below it. This will help to maintain the home exterior’s defense against rain and water runoff, and any siding replacement will be less noticeable below the window than above it.
If necessary, add spacer blocks to the rough opening sill to elevate the new window up to the level line (Image 1).
Install an aluminum drip cap above the window opening even if the manufacturer claims the garden window does not require it. Tuck the drip cap underneath the siding so the drip edge extends out over the top of the window (Image 2).
Lift the garden window up to the scaffolding and place it into the opening. Ensure that the window is level, vertically plumb and centered in the opening.
Insert tapered wood shims between the window and house framing to firmly position the window without forcing or bowing in the window sides. Double-check the window alignment in all dimensions, then screw through the window sides and shims into the house framing (Image 3).
On the outside of the window, attach mounting brackets provided by the manufacturer and fasten them to the house sheathing or framing for added support.
Cover up any gap in the house sheathing below the window and install siding to match the original.
Measure, cut and install the garden window’s exterior trim according to the manufacturer’s instructions.
Caulk around the window to complete the work on the outside (Image 1).
Inside, fill the space between the window frame and rough opening with insulation to prevent drafts (Image 2).
Measure, cut and attach the interior casing with finishing nails. Use wood filler to hide the holes and paint or stain the wood as needed Image 3).
Install any clips or brackets provided to hold the garden window’s glass shelf. Add plants and enjoy the view.