Measure the existing window opening and confirm the replacement window size
Remove the old window sash, stops, and trim as needed
Inspect the opening for rot, damage, or debris
Repair any damaged framing and ensure the opening is square
Apply flashing tape or waterproofing material where needed
Dry-fit the replacement window to confirm proper fit
Apply a continuous bead of exterior-grade sealant around the opening
Set the replacement window into the opening
Center and level the window
Shim the window at the sides and bottom until plumb, level, and square
Fasten the window through the manufacturer’s nailing fins or mounting holes
Recheck alignment before fully tightening fasteners
Seal around the exterior perimeter with flashing tape and/or sealant
Install insulation around the interior gap if required
Reinstall interior trim or casing
Seal interior gaps with caulk
Test the window to ensure it opens, closes, and locks properly