Measure the window opening
Remove the old window if needed
Inspect and repair the rough opening
Check that the opening is square, level, and plumb
Apply flashing or waterproofing as needed
Dry-fit the new window
Apply sealant or flashing tape to the sill
Set the window into the opening
Center and level the window
Shim the window until it is plumb, level, and square
Fasten the window according to the manufacturer’s instructions
Recheck alignment after fastening
Insulate gaps around the frame
Install interior and exterior trim
Seal exterior edges with caulk
Test the window for proper operation